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erlang(3erl)			     Erlang Module Definition			     erlang(3erl)

NAME
       erlang - The Erlang BIFs

DESCRIPTION
       By  convention,	most built-in functions (BIFs) are seen as being in the module erlang . A
       number of the BIFs are viewed more or less as part of the Erlang programming language  and
       are  auto-imported  .  Thus,  it  is not necessary to specify the module name and both the
       calls atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical.

       In the text, auto-imported BIFs are listed without module prefix. BIFs listed with  module
       prefix are not auto-imported.

       BIFs  may  fail	for  a	variety  of reasons. All BIFs fail with reason badarg if they are
       called with arguments of an incorrect type. The other reasons that may make BIFs fail  are
       described in connection with the description of each individual BIF.

       Some BIFs may be used in guard tests, these are marked with "Allowed in guard tests".

DATA TYPES
       ext_binary()
	 a binary data object,
	 structured according to the Erlang external term format

       iodata() = iolist() | binary()

       iolist() = [char() | binary() | iolist()]
	 a binary is allowed as the tail of the list

EXPORTS
       abs(Number) -> int() | float()

	      Types  Number = number()

	      Returns an integer or float which is the arithmetical absolute value of Number .

	      > abs(-3.33).
	      3.33
	      > abs(-3).
	      3

	      Allowed in guard tests.

       erlang:adler32(Data) -> int()

	      Types  Data = iodata()

	      Computes and returns the adler32 checksum for Data .

       erlang:adler32(OldAdler, Data) -> int()

	      Types  OldAdler = int()
		     Data = iodata()

	      Continue	computing  the	adler32  checksum  by  combining  the  previous checksum,
	      OldAdler , with the checksum of Data .

	      The following code:

		   X = erlang:adler32(Data1),
		   Y = erlang:adler32(X,Data2).

	      - would assign the same value to Y as this would:

		   Y = erlang:adler32([Data1,Data2]).

       erlang:adler32_combine(FirstAdler, SecondAdler, SecondSize) -> int()

	      Types  FirstAdler = SecondAdler = int()
		     SecondSize = int()

	      Combines two previously computed adler32 checksums. This computation  requires  the
	      size of the data object for the second checksum to be known.

	      The following code:

		   Y = erlang:adler32(Data1),
		   Z = erlang:adler32(Y,Data2).

	      - would assign the same value to Z as this would:

		   X = erlang:adler32(Data1),
		   Y = erlang:adler32(Data2),
		   Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).

       erlang:append_element(Tuple1, Term) -> Tuple2

	      Types  Tuple1 = Tuple2 = tuple()
		     Term = term()

	      Returns  a new tuple which has one element more than Tuple1 , and contains the ele-
	      ments in Tuple1 followed by Term as the last element.  Semantically  equivalent  to
	      list_to_tuple(tuple_to_list(Tuple) ++ [Term]) , but much faster.

	      > erlang:append_element({one, two}, three).
	      {one,two,three}

       apply(Fun, Args) -> term() | empty()

	      Types  Fun = fun()
		     Args = [term()]

	      Call a fun, passing the elements in Args as arguments.

	      Note:  If  the  number  of elements in the arguments are known at compile-time, the
	      call is better written as Fun(Arg1, Arg2, ... ArgN) .

   Warning:
       Earlier, Fun could also be given as {Module, Function} , equivalent to apply(Module, Func-
       tion,  Args)  .	This  usage  is  deprecated  and will stop working in a future release of
       Erlang/OTP.

       apply(Module, Function, Args) -> term() | empty()

	      Types  Module = Function = atom()
		     Args = [term()]

	      Returns the result of applying Function in Module to Args .  The	applied  function
	      must be exported from Module . The arity of the function is the length of Args .

	      > apply(lists, reverse, [[a, b, c]]).
	      [c,b,a]

	      apply can be used to evaluate BIFs by using the module name erlang .

	      > apply(erlang, atom_to_list, ['Erlang']).
	      "Erlang"

	      Note:  If  the  number  of  arguments are known at compile-time, the call is better
	      written as Module:Function(Arg1, Arg2, ..., ArgN) .

	      Failure: error_handler:undefined_function/3 is called if the  applied  function  is
	      not  exported.  The  error  handler  can be redefined (see process_flag/2 ). If the
	      error_handler is undefined, or if the user has redefined the default  error_handler
	      so  the  replacement  module is undefined, an error with the reason undef is gener-
	      ated.

       atom_to_binary(Atom, Encoding) -> binary()

	      Types  Atom = atom()
		     Encoding = latin1 | utf8 | unicode

	      Returns a binary which corresponds to the text representation of Atom . If Encoding
	      is  latin1  , there will be one byte for each character in the text representation.
	      If Encoding is utf8 or unicode , the characters will encoded using  UTF-8  (meaning
	      that characters from 16#80 up to 0xFF will be encode in two bytes).

   Note:
       Currently,  atom_to_binary(Atom, latin1) can never fail because the text representation of
       an atom can only contain characters from 0 to 16#FF. In a future release, the text  repre-
       sentation   of	atoms	might	be   allowed   to   contain  any  Unicode  character  and
       atom_to_binary(Atom, latin1) will fail if the text representation for the Atom contains	a
       Unicode character greater than 16#FF.

       > atom_to_binary('Erlang', latin1).
       <<"Erlang">>

       atom_to_list(Atom) -> string()

	      Types  Atom = atom()

	      Returns a string which corresponds to the text representation of Atom .

	      > atom_to_list('Erlang').
	      "Erlang"

       binary_part(Subject, PosLen) -> binary()

	      Types  Subject = binary()
		     PosLen = {Start,Length}
		     Start = int()
		     Length = int()

	      Extracts the part of the binary described by PosLen .

	      Negative length can be used to extract bytes at the end of a binary:

	      1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
	      2> binary_part(Bin,{byte_size(Bin), -5)).
	      <<6,7,8,9,10>>

	      If PosLen in any way references outside the binary, a badarg exception is raised.

	      Start is zero-based, i.e:

	      1> Bin = <<1,2,3>>
	      2> binary_part(Bin,{0,2}).
	      <<1,2>>

	      See the STDLIB module binary for details about the PosLen semantics.

	      Allowed in guard tests.

       binary_part(Subject, Start, Length) -> binary()

	      Types  Subject = binary()
		     Start = int()
		     Length = int()

	      The same as binary_part(Subject, {Pos, Len}) .

	      Allowed in guard tests.

       binary_to_atom(Binary, Encoding) -> atom()

	      Types  Binary = binary()
		     Encoding = latin1 | utf8 | unicode

	      Returns  the  atom whose text representation is Binary . If Encoding is latin1 , no
	      translation of bytes in the binary is done. If Encoding is utf8 or  unicode  ,  the
	      binary  must contain valid UTF-8 sequences; furthermore, only Unicode characters up
	      to 0xFF are allowed.

   Note:
       binary_to_atom(Binary, utf8) will fail if the binary contains Unicode  characters  greater
       than   16#FF.  In  a  future  release,  such  Unicode  characters  might  be  allowed  and
       binary_to_atom(Binary, utf8) will not fail in that case.

       > binary_to_atom(<<"Erlang">>, latin1).
       > binary_to_atom(<<1024/utf8>>, utf8).
       ** exception error: bad argument
	    in function  binary_to_atom/2
	       called as binary_to_atom(<<208,128>>,utf8)

       binary_to_existing_atom(Binary, Encoding) -> atom()

	      Types  Binary = binary()
		     Encoding = latin1 | utf8 | unicode

	      Works like binary_to_atom/2 , but the atom must already exist.

	      Failure: badarg if the atom does not already exist.

       binary_to_list(Binary) -> [char()]

	      Types  Binary = binary()

	      Returns a list of integers which correspond to the bytes of Binary .

       binary_to_list(Binary, Start, Stop) -> [char()]

	      Types  Binary = binary()
		     Start = Stop = 1..byte_size(Binary)

	      As binary_to_list/1 , but returns a list of integers  corresponding  to  the  bytes
	      from  position  Start to position Stop in Binary . Positions in the binary are num-
	      bered starting from 1.

   Note:
       This function's indexing style of using one-based indices for binaries is deprecated.  New
       code  should  use the functions in the STDLIB module binary instead. They consequently use
       the same (zero-based) style of indexing.

       bitstring_to_list(Bitstring) -> [char()|bitstring()]

	      Types  Bitstring = bitstring()

	      Returns a list of integers which correspond to the bytes of Bitstring . If the num-
	      ber  of bits in the binary is not divisible by 8, the last element of the list will
	      be a bitstring containing the remaining bits (1 up to 7 bits).

       binary_to_term(Binary) -> term()

	      Types  Binary = ext_binary()

	      Returns an Erlang term which is the result of decoding the binary object	Binary	,
	      which must be encoded according to the Erlang external term format.

   Warning:
       When  decoding binaries from untrusted sources, consider using binary_to_term/2 to prevent
       denial of service attacks.

       See also term_to_binary/1 and binary_to_term/2 .

       binary_to_term(Binary, Opts) -> term()

	      Types  Opts = [safe]
		     Binary = ext_binary()

	      As binary_to_term/1 , but takes options that affect decoding of the binary.

		safe :
		  Use this option when receiving binaries from an untrusted source.

		  When enabled, it prevents decoding data that may be used to attack  the  Erlang
		  system.  In  the  event  of receiving unsafe data, decoding fails with a badarg
		  error.

		  Currently, this prevents creation of new atoms directly, creation of new  atoms
		  indirectly  (as  they are embedded in certain structures like pids, refs, funs,
		  etc.), and  creation	of  new  external  function  references.  None	of  those
		  resources  are  currently  garbage collected, so unchecked creation of them can
		  exhaust available memory.

	      Failure: badarg if safe is specified and unsafe data is decoded.

	      See also term_to_binary/1 , binary_to_term/1 , and list_to_existing_atom/1 .

       bit_size(Bitstring) -> int()

	      Types  Bitstring = bitstring()

	      Returns an integer which is the size in bits of Bitstring .

	      > bit_size(<<433:16,3:3>>).
	      19
	      > bit_size(<<1,2,3>>).
	      24

	      Allowed in guard tests.

       erlang:bump_reductions(Reductions) -> void()

	      Types  Reductions = int()

	      This implementation-dependent function increments the  reduction	counter  for  the
	      calling  process.  In  the  Beam emulator, the reduction counter is normally incre-
	      mented by one for each function and BIF call, and a context switch is  forced  when
	      the counter reaches the maximum number of reductions for a process (2000 reductions
	      in R12B).

   Warning:
       This BIF might be removed in a future version of the Beam machine without  prior  warning.
       It is unlikely to be implemented in other Erlang implementations.

       byte_size(Bitstring) -> int()

	      Types  Bitstring = bitstring()

	      Returns an integer which is the number of bytes needed to contain Bitstring . (That
	      is, if the number of bits in Bitstring is not divisible by 8, the resulting  number
	      of bytes will be rounded up .)

	      > byte_size(<<433:16,3:3>>).
	      3
	      > byte_size(<<1,2,3>>).
	      3

	      Allowed in guard tests.

       erlang:cancel_timer(TimerRef) -> Time | false

	      Types  TimerRef = reference()
		     Time = int()

	      Cancels  a  timer,  where  TimerRef  was	returned by either erlang:send_after/3 or
	      erlang:start_timer/3 . If the timer is there to be removed,  the	function  returns
	      the  time  in milliseconds left until the timer would have expired, otherwise false
	      (which means that TimerRef was never a timer, that it has already  been  cancelled,
	      or that it has already delivered its message).

	      See also erlang:send_after/3 , erlang:start_timer/3 , and erlang:read_timer/1 .

	      Note:  Cancelling  a timer does not guarantee that the message has not already been
	      delivered to the message queue.

       check_process_code(Pid, Module) -> bool()

	      Types  Pid = pid()
		     Module = atom()

	      Returns true if the process Pid is executing old code for Module . That is, if  the
	      current  call  of  the process executes old code for this module, or if the process
	      has references to old code for this module, or if the process  contains  funs  that
	      references old code for this module. Otherwise, it returns false .

	      > check_process_code(Pid, lists).
	      false

	      See also code(3erl) .

       concat_binary(ListOfBinaries)

	      Do not use; use list_to_binary/1 instead.

       erlang:crc32(Data) -> int()

	      Types  Data = iodata()

	      Computes and returns the crc32 (IEEE 802.3 style) checksum for Data .

       erlang:crc32(OldCrc, Data) -> int()

	      Types  OldCrc = int()
		     Data = iodata()

	      Continue	computing the crc32 checksum by combining the previous checksum, OldCrc ,
	      with the checksum of Data .

	      The following code:

		   X = erlang:crc32(Data1),
		   Y = erlang:crc32(X,Data2).

	      - would assign the same value to Y as this would:

		   Y = erlang:crc32([Data1,Data2]).

       erlang:crc32_combine(FirstCrc, SecondCrc, SecondSize) -> int()

	      Types  FirstCrc = SecondCrc = int()
		     SecondSize = int()

	      Combines two previously computed crc32 checksums.  This  computation  requires  the
	      size of the data object for the second checksum to be known.

	      The following code:

		   Y = erlang:crc32(Data1),
		   Z = erlang:crc32(Y,Data2).

	      - would assign the same value to Z as this would:

		   X = erlang:crc32(Data1),
		   Y = erlang:crc32(Data2),
		   Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).

       date() -> {Year, Month, Day}

	      Types  Year = Month = Day = int()

	      Returns the current date as {Year, Month, Day} .

	      The time zone and daylight saving time correction depend on the underlying OS.

	      > date().
	      {1995,2,19}

       erlang:decode_packet(Type,Bin,Options)  ->  {ok,Packet,Rest} | {more,Length} | {error,Rea-
       son}

	      Types  Bin = binary()
		     Options = [Opt]
		     Packet = binary() | HttpPacket
		     Rest = binary()
		     Length = int() | undefined
		     Reason = term()
		     Type, Opt -- see below

		     HttpPacket = HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError
		     HttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}
		     HttpResponse = {http_response, HttpVersion, integer(), HttpString}
		     HttpHeader = {http_header, int(),	HttpField,  Reserved=term(),  Value=Http-
		     String}
		     HttpError = {http_error, HttpString}
		     HttpMethod = HttpMethodAtom | HttpString
		     HttpMethodAtom  =	'OPTIONS'  | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' |
		     'TRACE'
		     HttpUri = '*' | {absoluteURI, http|https, Host=HttpString,  Port=int()|unde-
		     fined,   Path=HttpString}	 |   {scheme,  Scheme=HttpString,  HttpString}	|
		     {abs_path, HttpString} | HttpString
		     HttpVersion = {Major=int(), Minor=int()}
		     HttpString = string() | binary()
		     HttpField = HttpFieldAtom | HttpString
		     HttpFieldAtom = 'Cache-Control' | 'Connection' | 'Date' | 'Pragma' | 'Trans-
		     fer-Encoding'  |  'Upgrade' | 'Via' | 'Accept' | 'Accept-Charset' | 'Accept-
		     Encoding' | 'Accept-Language' | 'Authorization' | 'From' | 'Host' | 'If-Mod-
		     ified-Since'  |  'If-Match' | 'If-None-Match' | 'If-Range' | 'If-Unmodified-
		     Since' | 'Max-Forwards' | 'Proxy-Authorization'  |  'Range'  |  'Referer'	|
		     'User-Agent'  |  'Age'  |	'Location'  |  'Proxy-Authenticate'  | 'Public' |
		     'Retry-After' | 'Server' | 'Vary' | 'Warning' | 'Www-Authenticate' | 'Allow'
		     |	'Content-Base'	|  'Content-Encoding'  |  'Content-Language'  | 'Content-
		     Length' | 'Content-Location' | 'Content-Md5' | 'Content-Range'  |	'Content-
		     Type'  |  'Etag'  |  'Expires'  |	'Last-Modified' | 'Accept-Ranges' | 'Set-
		     Cookie' | 'Set-Cookie2' | 'X-Forwarded-For'  |  'Cookie'  |  'Keep-Alive'	|
		     'Proxy-Connection'

	      Decodes  the  binary  Bin according to the packet protocol specified by Type . Very
	      similar to the packet handling done by sockets with the option {packet,Type}.

	      If an entire packet is contained in Bin it is returned together with the	remainder
	      of the binary as {ok,Packet,Rest} .

	      If  Bin  does  not  contain the entire packet, {more,Length} is returned. Length is
	      either the expected total size of the packet or undefined if  the  expected  packet
	      size is not known. decode_packet can then be called again with more data added.

	      If the packet does not conform to the protocol format {error,Reason} is returned.

	      The following values of Type are valid:

		raw | 0 :
		  No packet handling is done. Entire binary is returned unless it is empty.

		1 | 2 | 4 :
		  Packets  consist of a header specifying the number of bytes in the packet, fol-
		  lowed by that number of bytes. The length of header can be one,  two,  or  four
		  bytes;  the  order  of the bytes is big-endian. The header will be stripped off
		  when the packet is returned.

		line :
		  A packet is a line terminated with newline. The newline character  is  included
		  in  the  returned  packet unless the line was truncated according to the option
		  line_length .

		asn1 | cdr | sunrm | fcgi | tpkt :
		  The header is not stripped off.

		  The meanings of the packet types are as follows:

		  asn1 - ASN.1 BER :

		  sunrm - Sun's RPC encoding :

		  cdr - CORBA (GIOP 1.1) :

		  fcgi - Fast CGI :

		  tpkt - TPKT format [RFC1006] :

		http | httph | http_bin | httph_bin :
		  The Hypertext Transfer Protocol. The	packets  are  returned	with  the  format
		  according  to  HttpPacket  described	above.	A  packet  is either a request, a
		  response, a header or an end of header mark.	Invalid  lines	are  returned  as
		  HttpError .

		  Recognized  request methods and header fields are returned as atoms. Others are
		  returned as strings.

		  The protocol type http should only be used for the first line  when  a  HttpRe-
		  quest  or  a	HttpResponse is expected. The following calls should use httph to
		  get HttpHeader 's until http_eoh is returned that marks the end of the  headers
		  and the beginning of any following message body.

		  The variants http_bin and httph_bin will return strings ( HttpString ) as bina-
		  ries instead of lists.

	      The following options are available:

		{packet_size, int()} :
		  Sets the max allowed size of the packet body. If the	packet	header	indicates
		  that the length of the packet is longer than the max allowed length, the packet
		  is considered invalid. Default is 0 which means no size limit.

		{line_length, int()} :
		  Applies only to line oriented protocols ( line , http ). Lines longer than this
		  will be truncated.

	      > erlang:decode_packet(1,<<3,"abcd">>,[]).
	      {ok,<<"abc">>,<<"d">>}
	      > erlang:decode_packet(1,<<5,"abcd">>,[]).
	      {more,6}

       delete_module(Module) -> true | undefined

	      Types  Module = atom()

	      Makes  the  current code for Module become old code, and deletes all references for
	      this module from the export table. Returns undefined if the module does not  exist,
	      otherwise true .

   Warning:
       This  BIF  is  intended for the code server (see code(3erl) ) and should not be used else-
       where.

       Failure: badarg if there is already an old version of Module .

       demonitor(MonitorRef) -> true

	      Types  MonitorRef = reference()

	      If MonitorRef is a reference which the calling process obtained  by  calling  moni-
	      tor/2  ,	this  monitoring  is turned off. If the monitoring is already turned off,
	      nothing happens.

	      Once demonitor(MonitorRef) has returned it is guaranteed that no {'DOWN',  Monitor-
	      Ref,  _,	_,  _}	message  due to the monitor will be placed in the callers message
	      queue in the future. A {'DOWN', MonitorRef, _, _, _} message might have been placed
	      in  the  callers message queue prior to the call, though. Therefore, in most cases,
	      it is advisable to remove such a 'DOWN' message from the message queue after  moni-
	      toring  has  been  stopped.  demonitor(MonitorRef,  [flush]) can be used instead of
	      demonitor(MonitorRef) if this cleanup is wanted.

   Note:
       Prior to OTP release R11B (erts version 5.5) demonitor/1 behaved completely  asynchronous,
       i.e.,  the  monitor  was active until the "demonitor signal" reached the monitored entity.
       This had one undesirable effect, though. You could never know when you were guaranteed not
       to receive a DOWN message due to the monitor.

       Current	behavior can be viewed as two combined operations: asynchronously send a "demoni-
       tor signal" to the monitored entity and ignore any future results of the monitor.

       Failure: It is an error if MonitorRef refers to a monitoring started by	another  process.
       Not  all  such  cases are cheap to check; if checking is cheap, the call fails with badarg
       (for example if MonitorRef is a remote reference).

       demonitor(MonitorRef, OptionList) -> true|false

	      Types  MonitorRef = reference()
		     OptionList = [Option]
		     Option = flush
		     Option = info

	      The returned value is true unless info is part of OptionList .

	      demonitor(MonitorRef, []) is equivalent to demonitor(MonitorRef) .

	      Currently the following Option s are valid:

		flush :
		  Remove (one) {_, MonitorRef, _, _, _} message, if there is one, from the  call-
		  ers message queue after monitoring has been stopped.

		  Calling demonitor(MonitorRef, [flush]) is equivalent to the following, but more
		  efficient:

		    demonitor(MonitorRef),
		    receive
			{_, MonitorRef, _, _, _} ->
			    true
		    after 0 ->
			    true
		    end

		info :
		  The returned value is one of the following:

		  true :
		    The monitor was found and removed. In this case no 'DOWN' message due to this
		    monitor have been nor will be placed in the message queue of the caller.

		  false :
		    The  monitor  was  not  found and could not be removed. This probably because
		    someone already has placed a 'DOWN' message corresponding to this monitor  in
		    the callers message queue.

		  If the info option is combined with the flush option, false will be returned if
		  a flush was needed; otherwise, true .

   Note:
       More options may be added in the future.

       Failure: badarg if OptionList is not a list, or if Option is not a valid  option,  or  the
       same failure as for demonitor/1

       disconnect_node(Node) -> bool() | ignored

	      Types  Node = atom()

	      Forces  the  disconnection  of  a node. This will appear to the node Node as if the
	      local node has crashed. This BIF is mainly used in the Erlang  network  authentica-
	      tion  protocols.	Returns  true if disconnection succeeds, otherwise false . If the
	      local node is not alive, the function returns ignored .

       erlang:display(Term) -> true

	      Types  Term = term()

	      Prints a text representation of Term on the standard output.

   Warning:
       This BIF is intended for debugging only.

       element(N, Tuple) -> term()

	      Types  N = 1..tuple_size(Tuple)
		     Tuple = tuple()

	      Returns the N th element (numbering from 1) of Tuple .

	      > element(2, {a, b, c}).
	      b

	      Allowed in guard tests.

       erase() -> [{Key, Val}]

	      Types  Key = Val = term()

	      Returns the process dictionary and deletes it.

	      > put(key1, {1, 2, 3}),
	      put(key2, [a, b, c]),
	      erase().
	      [{key1,{1,2,3}},{key2,[a,b,c]}]

       erase(Key) -> Val | undefined

	      Types  Key = Val = term()

	      Returns the value Val associated with Key and deletes it from the  process  dictio-
	      nary. Returns undefined if no value is associated with Key .

	      > put(key1, {merry, lambs, are, playing}),
	      X = erase(key1),
	      {X, erase(key1)}.
	      {{merry,lambs,are,playing},undefined}

       error(Reason)

	      Types  Reason = term()

	      Stops the execution of the calling process with the reason Reason , where Reason is
	      any term. The actual exit reason will be {Reason, Where} , where Where is a list of
	      the  functions  most recently called (the current function first). Since evaluating
	      this function causes the process to terminate, it has no return value.

	      > catch error(foobar).
	      {'EXIT',{foobar,[{erl_eval,do_apply,5},
			       {erl_eval,expr,5},
			       {shell,exprs,6},
			       {shell,eval_exprs,6},
			       {shell,eval_loop,3}]}}

       error(Reason, Args)

	      Types  Reason = term()
		     Args = [term()]

	      Stops the execution of the calling process with the reason Reason , where Reason is
	      any term. The actual exit reason will be {Reason, Where} , where Where is a list of
	      the functions most recently called (the current function first). Args  is  expected
	      to  be  the  list of arguments for the current function; in Beam it will be used to
	      provide the actual arguments for the current function  in  the  Where  term.  Since
	      evaluating this function causes the process to terminate, it has no return value.

       exit(Reason)

	      Types  Reason = term()

	      Stops the execution of the calling process with the exit reason Reason , where Rea-
	      son is any term. Since evaluating this function causes the process to terminate, it
	      has no return value.

	      > exit(foobar).
	      ** exception exit: foobar
	      > catch exit(foobar).
	      {'EXIT',foobar}

       exit(Pid, Reason) -> true

	      Types  Pid = pid()
		     Reason = term()

	      Sends an exit signal with exit reason Reason to the process Pid .

	      The following behavior apply if Reason is any term except normal or kill :

	      If Pid is not trapping exits, Pid itself will exit with exit reason Reason . If Pid
	      is trapping exits, the exit signal is transformed into  a  message  {'EXIT',  From,
	      Reason}  and delivered to the message queue of Pid . From is the pid of the process
	      which sent the exit signal. See also process_flag/2 .

	      If Reason is the atom normal , Pid will not exit. If it is trapping exits, the exit
	      signal  is  transformed  into a message {'EXIT', From, normal} and delivered to its
	      message queue.

	      If Reason is the atom kill , that is if exit(Pid, kill) is called,  an  untrappable
	      exit  signal is sent to Pid which will unconditionally exit with exit reason killed
	      .

       float(Number) -> float()

	      Types  Number = number()

	      Returns a float by converting Number to a float.

	      > float(55).
	      55.0

	      Allowed in guard tests.

   Note:
       Note that if used on the top-level in a guard, it will test  whether  the  argument  is	a
       floating point number; for clarity, use is_float/1 instead.

       When float/1 is used in an expression in a guard, such as ' float(A) == 4.0 ', it converts
       a number as described above.

       float_to_list(Float) -> string()

	      Types  Float = float()

	      Returns a string which corresponds to the text representation of Float .

	      > float_to_list(7.0).
	      "7.00000000000000000000e+00"

       erlang:fun_info(Fun) -> [{Item, Info}]

	      Types  Fun = fun()
		     Item, Info -- see below

	      Returns a list containing information about the fun Fun . Each element of the  list
	      is a tuple. The order of the tuples is not defined, and more tuples may be added in
	      a future release.

   Warning:
       This BIF is mainly intended for debugging, but it can occasionally be  useful  in  library
       functions that might need to verify, for instance, the arity of a fun.

       There are two types of funs with slightly different semantics:

       A  fun  created	by  fun  M:F/A is called an external fun. Calling it will always call the
       function F with arity A in the latest code for module M . Note that module M does not even
       need to be loaded when the fun fun M:F/A is created.

       All other funs are called local . When a local fun is called, the same version of the code
       that created the fun will be called (even if newer version of the module has been loaded).

       The following elements will always be present in the list  for  both  local  and  external
       funs:

	 {type, Type} :
	   Type is either local or external .

	 {module, Module} :
	   Module (an atom) is the module name.

	   If Fun is a local fun, Module is the module in which the fun is defined.

	   If Fun is an external fun, Module is the module that the fun refers to.

	 {name, Name} :
	   Name (an atom) is a function name.

	   If Fun is a local fun, Name is the name of the local function that implements the fun.
	   (This name was generated by the compiler, and is generally only of informational  use.
	   As it is a local function, it is not possible to call it directly.) If no code is cur-
	   rently loaded for the fun, [] will be returned instead of an atom.

	   If Fun is an external fun, Name is the name of the  exported  function  that  the  fun
	   refers to.

	 {arity, Arity} :
	   Arity is the number of arguments that the fun should be called with.

	 {env, Env} :
	   Env (a list) is the environment or free variables for the fun. (For external funs, the
	   returned list is always empty.)

       The following elements will only be present in the list if Fun is local:

	 {pid, Pid} :
	   Pid is the pid of the process that originally created the fun.

	 {index, Index} :
	   Index (an integer) is an index into the module's fun table.

	 {new_index, Index} :
	   Index (an integer) is an index into the module's fun table.

	 {new_uniq, Uniq} :
	   Uniq (a binary) is a unique value for this fun.

	 {uniq, Uniq} :
	   Uniq (an integer) is a unique value for this fun.

       erlang:fun_info(Fun, Item) -> {Item, Info}

	      Types  Fun = fun()
		     Item, Info -- see below

	      Returns information about Fun as specified by Item , in the form {Item,Info} .

	      For any fun, Item can be any of the atoms module , name , arity , or env .

	      For a local fun, Item can also be any of the atoms index , new_index ,  new_uniq	,
	      uniq , and pid . For an external fun, the value of any of these items is always the
	      atom undefined .

	      See erlang:fun_info/1 .

       erlang:fun_to_list(Fun) -> string()

	      Types  Fun = fun()

	      Returns a string which corresponds to the text representation of Fun .

       erlang:function_exported(Module, Function, Arity) -> bool()

	      Types  Module = Function = atom()
		     Arity = int()

	      Returns true if the module Module is loaded and contains an exported function Func-
	      tion/Arity ; otherwise false .

	      Returns false for any BIF (functions implemented in C rather than in Erlang).

       garbage_collect() -> true

	      Forces  an  immediate  garbage  collection  of the currently executing process. The
	      function should not be used, unless it has been noticed -- or there are  good  rea-
	      sons  to	suspect -- that the spontaneous garbage collection will occur too late or
	      not at all. Improper use may seriously degrade system performance.

	      Compatibility note: In versions of OTP prior to R7,  the	garbage  collection  took
	      place  at the next context switch, not immediately. To force a context switch after
	      a call to erlang:garbage_collect() , it was sufficient to make any function call.

       garbage_collect(Pid) -> bool()

	      Types  Pid = pid()

	      Works like erlang:garbage_collect() but on any process.  The  same  caveats  apply.
	      Returns false if Pid refers to a dead process; true otherwise.

       get() -> [{Key, Val}]

	      Types  Key = Val = term()

	      Returns the process dictionary as a list of {Key, Val} tuples.

	      > put(key1, merry),
	      put(key2, lambs),
	      put(key3, {are, playing}),
	      get().
	      [{key1,merry},{key2,lambs},{key3,{are,playing}}]

       get(Key) -> Val | undefined

	      Types  Key = Val = term()

	      Returns  the  value Val associated with Key in the process dictionary, or undefined
	      if Key does not exist.

	      > put(key1, merry),
	      put(key2, lambs),
	      put({any, [valid, term]}, {are, playing}),
	      get({any, [valid, term]}).
	      {are,playing}

       erlang:get_cookie() -> Cookie | nocookie

	      Types  Cookie = atom()

	      Returns the magic cookie of the local node, if the node  is  alive;  otherwise  the
	      atom nocookie .

       get_keys(Val) -> [Key]

	      Types  Val = Key = term()

	      Returns  a list of keys which are associated with the value Val in the process dic-
	      tionary.

	      > put(mary, {1, 2}),
	      put(had, {1, 2}),
	      put(a, {1, 2}),
	      put(little, {1, 2}),
	      put(dog, {1, 3}),
	      put(lamb, {1, 2}),
	      get_keys({1, 2}).
	      [mary,had,a,little,lamb]

       erlang:get_stacktrace() -> [{Module, Function, Arity | Args}]

	      Types  Module = Function = atom()
		     Arity = int()
		     Args = [term()]

	      Get the call stack back-trace ( stacktrace ) of the last exception in  the  calling
	      process  as  a list of {Module,Function,Arity} tuples. The Arity field in the first
	      tuple may be the argument list of that function call instead of an  arity  integer,
	      depending on the exception.

	      If  there  has  not been any exceptions in a process, the stacktrace is []. After a
	      code change for the process, the stacktrace may also be reset to [].

	      The stacktrace is the same data as the catch operator returns, for example:

	      {'EXIT',{badarg,Stacktrace}} = catch abs(x)

	      See also erlang:error/1 and erlang:error/2 .

       group_leader() -> GroupLeader

	      Types  GroupLeader = pid()

	      Returns the pid of the group leader for the process which evaluates the function.

	      Every process is a member of some process group and all groups have a group  leader
	      .  All  IO  from	the group is channeled to the group leader. When a new process is
	      spawned, it gets the same group leader as the spawning process. Initially, at  sys-
	      tem  start-up,  init  is both its own group leader and the group leader of all pro-
	      cesses.

       group_leader(GroupLeader, Pid) -> true

	      Types  GroupLeader = Pid = pid()

	      Sets the group leader of Pid to GroupLeader . Typically, this is used when  a  pro-
	      cesses started from a certain shell should have another group leader than init .

	      See also group_leader/0 .

       halt()

	      Halts  the  Erlang runtime system and indicates normal exit to the calling environ-
	      ment. Has no return value.

	      > halt().
	      os_prompt%

       halt(Status)

	      Types  Status = int()>=0 | string()

	      Status must be a non-negative integer, or a string. Halts the Erlang  runtime  sys-
	      tem. Has no return value. If Status is an integer, it is returned as an exit status
	      of Erlang to the calling environment. If Status is a  string,  produces  an  Erlang
	      crash dump with String as slogan, and then exits with a non-zero status code.

	      Note that on many platforms, only the status codes 0-255 are supported by the oper-
	      ating system.

       erlang:hash(Term, Range) -> Hash

	      Returns a hash value for Term within the range 1..Range  .  The  allowed	range  is
	      1..2^27-1.

   Warning:
       This  BIF  is deprecated as the hash value may differ on different architectures. Also the
       hash values for integer terms larger than 2^27 as well as large binaries  are  very  poor.
       The  BIF  is  retained  for  backward compatibility reasons (it may have been used to hash
       records into a file), but all new code should  use  one	of  the  BIFs  erlang:phash/2  or
       erlang:phash2/1,2 instead.

       hd(List) -> term()

	      Types  List = [term()]

	      Returns the head of List , that is, the first element.

	      > hd([1,2,3,4,5]).
	      1

	      Allowed in guard tests.

	      Failure: badarg if List is the empty list [].

       erlang:hibernate(Module, Function, Args)

	      Types  Module = Function = atom()
		     Args = [term()]

	      Puts  the  calling  process  into a wait state where its memory allocation has been
	      reduced as much as possible, which is useful if the  process  does  not  expect  to
	      receive any messages in the near future.

	      The process will be awaken when a message is sent to it, and control will resume in
	      Module:Function with the arguments given by Args with the call stack emptied, mean-
	      ing  that the process will terminate when that function returns. Thus erlang:hiber-
	      nate/3 will never return to its caller.

	      If the process has any message in its message queue, the	process  will  be  awaken
	      immediately in the same way as described above.

	      In more technical terms, what erlang:hibernate/3 does is the following. It discards
	      the call stack for the process. Then it garbage collects	the  process.  After  the
	      garbage  collection,  all  live  data  is  in one continuous heap. The heap is then
	      shrunken to the exact same size as the live data which it holds (even if that  size
	      is less than the minimum heap size for the process).

	      If the size of the live data in the process is less than the minimum heap size, the
	      first garbage collection occurring after the process has been  awaken  will  ensure
	      that the heap size is changed to a size not smaller than the minimum heap size.

	      Note  that  emptying the call stack means that any surrounding catch is removed and
	      has to be re-inserted after hibernation. One  effect  of	this  is  that	processes
	      started  using proc_lib (also indirectly, such as gen_server processes), should use
	      proc_lib:hibernate/3 instead to ensure that the exception handler continues to work
	      when the process wakes up.

       integer_to_list(Integer) -> string()

	      Types  Integer = int()

	      Returns a string which corresponds to the text representation of Integer .

	      > integer_to_list(77).
	      "77"

       integer_to_list(Integer, Base) -> string()

	      Types  Integer = int()
		     Base = 2..36

	      Returns  a  string  which corresponds to the text representation of Integer in base
	      Base .

	      > integer_to_list(1023, 16).
	      "3FF"

       iolist_to_binary(IoListOrBinary) -> binary()

	      Types  IoListOrBinary = iolist() | binary()

	      Returns a binary which is made from the integers and binaries in IoListOrBinary .

	      > Bin1 = <<1,2,3>>.
	      <<1,2,3>>
	      > Bin2 = <<4,5>>.
	      <<4,5>>
	      > Bin3 = <<6>>.
	      <<6>>
	      > iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
	      <<1,2,3,1,2,3,4,5,4,6>>

       iolist_size(Item) -> int()

	      Types  Item = iolist() | binary()

	      Returns an integer which is the size in bytes of	the  binary  that  would  be  the
	      result of iolist_to_binary(Item) .

	      > iolist_size([1,2|<<3,4>>]).
	      4

       is_alive() -> bool()

	      Returns true if the local node is alive; that is, if the node can be part of a dis-
	      tributed system. Otherwise, it returns false .

       is_atom(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is an atom; otherwise returns false .

	      Allowed in guard tests.

       is_binary(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a binary; otherwise returns false .

	      A binary always contains a complete number of bytes.

	      Allowed in guard tests.

       is_bitstring(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a bitstring (including a binary); otherwise returns false .

	      Allowed in guard tests.

       is_boolean(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is either the atom true or the atom false  (i.e.  a	boolean);
	      otherwise returns false .

	      Allowed in guard tests.

       erlang:is_builtin(Module, Function, Arity) -> bool()

	      Types  Module = Function = atom()
		     Arity = int()

	      Returns  true if Module:Function/Arity is a BIF implemented in C; otherwise returns
	      false . This BIF is useful for builders of cross reference tools.

       is_float(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a floating point number; otherwise returns false .

	      Allowed in guard tests.

       is_function(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a fun; otherwise returns false .

	      Allowed in guard tests.

       is_function(Term, Arity) -> bool()

	      Types  Term = term()
		     Arity = int()

	      Returns true if Term is a fun that can be applied with Arity number  of  arguments;
	      otherwise returns false .

	      Allowed in guard tests.

   Warning:
       Currently,  is_function/2  will	also  return true if the first argument is a tuple fun (a
       tuple containing two atoms). In a future release, tuple funs will no longer  be	supported
       and is_function/2 will return false if given a tuple fun.

       is_integer(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is an integer; otherwise returns false .

	      Allowed in guard tests.

       is_list(Term) -> bool()

	      Types  Term = term()

	      Returns  true if Term is a list with zero or more elements; otherwise returns false
	      .

	      Allowed in guard tests.

       is_number(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is either an integer or a  floating	point  number;	otherwise
	      returns false .

	      Allowed in guard tests.

       is_pid(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a pid (process identifier); otherwise returns false .

	      Allowed in guard tests.

       is_port(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a port identifier; otherwise returns false .

	      Allowed in guard tests.

       is_process_alive(Pid) -> bool()

	      Types  Pid = pid()

	      Pid  must  refer to a process at the local node. Returns true if the process exists
	      and is alive, that is, is not exiting and has not exited. Otherwise, returns  false
	      .

       is_record(Term, RecordTag) -> bool()

	      Types  Term = term()
		     RecordTag = atom()

	      Returns  true  if  Term  is a tuple and its first element is RecordTag . Otherwise,
	      returns false .

   Note:
       Normally the compiler treats calls to is_record/2 specially. It emits code to verify  that
       Term  is a tuple, that its first element is RecordTag , and that the size is correct. How-
       ever, if the RecordTag is not a literal atom, the is_record/2 BIF will be  called  instead
       and the size of the tuple will not be verified.

       Allowed in guard tests, if RecordTag is a literal atom.

       is_record(Term, RecordTag, Size) -> bool()

	      Types  Term = term()
		     RecordTag = atom()
		     Size = int()

	      RecordTag  must  be  an atom. Returns true if Term is a tuple, its first element is
	      RecordTag , and its size is Size . Otherwise, returns false .

	      Allowed in guard tests, provided that RecordTag is a literal atom  and  Size  is	a
	      literal integer.

   Note:
       This BIF is documented for completeness. In most cases is_record/2 should be used.

       is_reference(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a reference; otherwise returns false .

	      Allowed in guard tests.

       is_tuple(Term) -> bool()

	      Types  Term = term()

	      Returns true if Term is a tuple; otherwise returns false .

	      Allowed in guard tests.

       length(List) -> int()

	      Types  List = [term()]

	      Returns the length of List .

	      > length([1,2,3,4,5,6,7,8,9]).
	      9

	      Allowed in guard tests.

       link(Pid) -> true

	      Types  Pid = pid() | port()

	      Creates  a  link between the calling process and another process (or port) Pid , if
	      there is not such a link already. If a process attempts to create a link to itself,
	      nothing is done. Returns true .

	      If Pid does not exist, the behavior of the BIF depends on if the calling process is
	      trapping exits or not (see process_flag/2 ):

		* If the calling process is not trapping exits, and checking Pid is cheap -- that
		  is, if Pid is local -- link/1 fails with reason noproc .

		* Otherwise,  if  the  calling	process  is trapping exits, and/or Pid is remote,
		  link/1 returns true , but an exit signal with reason	noproc	is  sent  to  the
		  calling process.

       list_to_atom(String) -> atom()

	      Types  String = string()

	      Returns the atom whose text representation is String .

	      > list_to_atom("Erlang").

       list_to_binary(IoList) -> binary()

	      Types  IoList = iolist()

	      Returns a binary which is made from the integers and binaries in IoList .

	      > Bin1 = <<1,2,3>>.
	      <<1,2,3>>
	      > Bin2 = <<4,5>>.
	      <<4,5>>
	      > Bin3 = <<6>>.
	      <<6>>
	      > list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
	      <<1,2,3,1,2,3,4,5,4,6>>

       list_to_bitstring(BitstringList) -> bitstring()

	      Types  BitstringList = [BitstringList | bitstring() | char()]

	      Returns a bitstring which is made from the integers and bitstrings in BitstringList
	      . (The last tail in BitstringList is allowed to be a bitstring.)

	      > Bin1 = <<1,2,3>>.
	      <<1,2,3>>
	      > Bin2 = <<4,5>>.
	      <<4,5>>
	      > Bin3 = <<6,7:4,>>.
	      <<6>>
	      > list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
	      <<1,2,3,1,2,3,4,5,4,6,7:46>>

       list_to_existing_atom(String) -> atom()

	      Types  String = string()

	      Returns the atom whose text representation is String , but only  if  there  already
	      exists such atom.

	      Failure:	badarg	if there does not already exist an atom whose text representation
	      is String .

       list_to_float(String) -> float()

	      Types  String = string()

	      Returns the float whose text representation is String .

	      > list_to_float("2.2017764e+0").
	      2.2017764

	      Failure: badarg if String contains a bad representation of a float.

       list_to_integer(String) -> int()

	      Types  String = string()

	      Returns an integer whose text representation is String .

	      > list_to_integer("123").
	      123

	      Failure: badarg if String contains a bad representation of an integer.

       list_to_integer(String, Base) -> int()

	      Types  String = string()
		     Base = 2..36

	      Returns an integer whose text representation in base Base is String .

	      > list_to_integer("3FF", 16).
	      1023

	      Failure: badarg if String contains a bad representation of an integer.

       list_to_pid(String) -> pid()

	      Types  String = string()

	      Returns a pid whose text representation is String .

   Warning:
       This BIF is intended for debugging and for use in the Erlang operating system.  It  should
       not be used in application programs.

       > list_to_pid("<0.4.1>").
       <0.4.1>

       Failure: badarg if String contains a bad representation of a pid.

       list_to_tuple(List) -> tuple()

	      Types  List = [term()]

	      Returns a tuple which corresponds to List . List can contain any Erlang terms.

	      > list_to_tuple([share, ['Ericsson_B', 163]]).
	      {share, ['Ericsson_B', 163]}

       load_module(Module, Binary) -> {module, Module} | {error, Reason}

	      Types  Module = atom()
		     Binary = binary()
		     Reason = badfile | not_purged | badfile

	      If  Binary  contains  the  object  code for the module Module , this BIF loads that
	      object code. Also, if the code for the module Module  already  exists,  all  export
	      references  are  replaced  so  they  point to the newly loaded code. The previously
	      loaded code is kept in the system as old code, as  there	may  still  be	processes
	      which are executing that code. It returns either {module, Module} , or {error, Rea-
	      son} if loading fails. Reason is one of the following:

		badfile :
		  The object code in Binary has an incorrect format.

		not_purged :
		  Binary contains a module which cannot be loaded because old code for this  mod-
		  ule already exists.

		badfile :
		  The object code contains code for another module than Module

   Warning:
       This  BIF  is  intended for the code server (see code(3erl) ) and should not be used else-
       where.

       erlang:load_nif(Path, LoadInfo) -> ok | {error, {Reason, Text}}

	      Types  Path = string()
		     LoadInfo = term()
		     Reason = load_failed | bad_lib | load | reload | upgrade | old_code
		     Text = string()

   Note:
       In releases older than OTP R14B, NIFs were an experimental feature. Versions of OTP  older
       than R14B might have different and possibly incompatible NIF semantics and interfaces. For
       example, in R13B03 the return value on failure was {error,Reason,Text} .

       Loads and links a dynamic library containing native implemented	functions  (NIFs)  for	a
       module.	Path  is  a  file  path to the sharable object/dynamic library file minus the OS-
       dependent file extension (.so for Unix and .dll for Windows). See erl_nif on how to imple-
       ment a NIF library.

       LoadInfo  can  be any term. It will be passed on to the library as part of the initializa-
       tion. A good practice is to include a module version number to support future code upgrade
       scenarios.

       The  call  to load_nif/2 must be made directly from the Erlang code of the module that the
       NIF library belongs to.

       It returns either ok , or {error,{Reason,Text}} if loading fails. Reason  is  one  of  the
       atoms  below,  while  Text  is a human readable string that may give some more information
       about the failure.

	 load_failed :
	   The OS failed to load the NIF library.

	 bad_lib :
	   The library did not fulfil the requirements as a NIF library of the calling module.

	 load | reload | upgrade :
	   The corresponding library callback was not successful.

	 old_code :
	   The call to load_nif/2 was made from the old code of a module that has been	upgraded.
	   This is not allowed.

       erlang:loaded() -> [Module]

	      Types  Module = atom()

	      Returns  a  list	of all loaded Erlang modules (current and/or old code), including
	      preloaded modules.

	      See also code(3erl) .

       erlang:localtime() -> {Date, Time}

	      Types  Date = {Year, Month, Day}
		     Time = {Hour, Minute, Second}
		     Year = Month = Day = Hour = Minute = Second = int()

	      Returns the current local date and time {{Year, Month, Day},  {Hour,  Minute,  Sec-
	      ond}} .

	      The time zone and daylight saving time correction depend on the underlying OS.

	      > erlang:localtime().
	      {{1996,11,6},{14,45,17}}

       erlang:localtime_to_universaltime({Date1, Time1}) -> {Date2, Time2}

	      Types  Date1 = Date2 = {Year, Month, Day}
		     Time1 = Time2 = {Hour, Minute, Second}
		     Year = Month = Day = Hour = Minute = Second = int()

	      Converts	local  date and time to Universal Time Coordinated (UTC), if this is sup-
	      ported by the underlying OS. Otherwise, no conversion is done and {Date1, Time1} is
	      returned.

	      > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
	      {{1996,11,6},{13,45,17}}

	      Failure: badarg if Date1 or Time1 do not denote a valid date or time.

       erlang:localtime_to_universaltime({Date1, Time1}, IsDst) -> {Date2, Time2}

	      Types  Date1 = Date2 = {Year, Month, Day}
		     Time1 = Time2 = {Hour, Minute, Second}
		     Year = Month = Day = Hour = Minute = Second = int()
		     IsDst = true | false | undefined

	      Converts	local  date  and  time	to  Universal  Time  Coordinated  (UTC) just like
	      erlang:localtime_to_universaltime/1 , but the caller  decides  if  daylight  saving
	      time is active or not.

	      If  IsDst  ==  true  the {Date1, Time1} is during daylight saving time, if IsDst ==
	      false it is not, and if IsDst == undefined the underlying OS may	guess,	which  is
	      the same as calling erlang:localtime_to_universaltime({Date1, Time1}) .

	      > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
	      {{1996,11,6},{12,45,17}}
	      > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
	      {{1996,11,6},{13,45,17}}
	      > erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
	      {{1996,11,6},{13,45,17}}

	      Failure: badarg if Date1 or Time1 do not denote a valid date or time.

       make_ref() -> reference()

	      Returns an almost unique reference.

	      The  returned  reference will re-occur after approximately 2^82 calls; therefore it
	      is unique enough for practical purposes.

	      > make_ref().
	      #Ref<0.0.0.135>

       erlang:make_tuple(Arity, InitialValue) -> tuple()

	      Types  Arity = int()
		     InitialValue = term()

	      Returns a new tuple of the given Arity , where all elements are InitialValue .

	      > erlang:make_tuple(4, []).
	      {[],[],[],[]}

       erlang:make_tuple(Arity, Default, InitList) -> tuple()

	      Types  Arity = int()
		     Default = term()
		     InitList = [{Position,term()}]
		     Position = integer()

	      erlang:make_tuple first creates a tuple of size Arity where each	element  has  the
	      value  Default  .  It  then  fills  in  values from InitList . Each list element in
	      InitList must be a two-tuple where the first element is a  position  in  the  newly
	      created  tuple  and  the second element is any term. If a position occurs more than
	      once in the list, the term corresponding to last occurrence will be used.

	      > erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).
	      {{[],aa,[],[],zz}

       max(Term1, Term2) -> Maximum

	      Types  Term1 = Term2 = Maximum = term()

	      Return the largest of Term1 and Term2 ; if the terms compares equal, Term1 will  be
	      returned.

       erlang:md5(Data) -> Digest

	      Types  Data = iodata()
		     Digest = binary()

	      Computes	an  MD5  message digest from Data , where the length of the digest is 128
	      bits (16 bytes). Data is a binary or a list of small integers and binaries.

	      See The MD5 Message Digest Algorithm (RFC 1321) for more information about MD5.

   Warning:
       The MD5 Message Digest Algorithm is not	considered  safe  for  code-signing  or  software
       integrity purposes.

       erlang:md5_final(Context) -> Digest

	      Types  Context = Digest = binary()

	      Finishes the update of an MD5 Context and returns the computed MD5 message digest.

       erlang:md5_init() -> Context

	      Types  Context = binary()

	      Creates an MD5 context, to be used in subsequent calls to md5_update/2 .

       erlang:md5_update(Context, Data) -> NewContext

	      Types  Data = iodata()
		     Context = NewContext = binary()

	      Updates an MD5 Context with Data , and returns a NewContext .

       erlang:memory() -> [{Type, Size}]

	      Types  Type, Size -- see below

	      Returns  a  list	containing  information about memory dynamically allocated by the
	      Erlang emulator. Each element of the list is a tuple {Type, Size} . The first  ele-
	      ment Type is an atom describing memory type. The second element Size is memory size
	      in bytes. A description of each memory type follows:

		total :
		  The total amount of memory currently allocated, which is the same as the sum of
		  memory size for processes and system .

		processes :
		  The total amount of memory currently allocated by the Erlang processes.

		processes_used :
		  The total amount of memory currently used by the Erlang processes.

		  This memory is part of the memory presented as processes memory.

		system :
		  The  total  amount  of  memory  currently allocated by the emulator that is not
		  directly related to any Erlang process.

		  Memory presented as processes is not included in this memory.

		atom :
		  The total amount of memory currently allocated for atoms.

		  This memory is part of the memory presented as system memory.

		atom_used :
		  The total amount of memory currently used for atoms.

		  This memory is part of the memory presented as atom memory.

		binary :
		  The total amount of memory currently allocated for binaries.

		  This memory is part of the memory presented as system memory.

		code :
		  The total amount of memory currently allocated for Erlang code.

		  This memory is part of the memory presented as system memory.

		ets :
		  The total amount of memory currently allocated for ets tables.

		  This memory is part of the memory presented as system memory.

		maximum :
		  The maximum total amount of memory allocated since the emulator was started.

		  This tuple is only present when the emulator is run with instrumentation.

		  For information on how to run the emulator  with  instrumentation  see  instru-
		  ment(3erl) and/or erl(1) .

   Note:
       The  system value is not complete. Some allocated memory that should be part of the system
       value are not.

       When the emulator is run with instrumentation, the system value is more accurate, but mem-
       ory  directly  allocated  by  malloc (and friends) are still not part of the system value.
       Direct calls to malloc are only done from OS specific runtime libraries and  perhaps  from
       user  implemented  Erlang  drivers  that do not use the memory allocation functions in the
       driver interface.

       Since the total value is the sum of processes and system the error in system  will  propa-
       gate to the total value.

       The  different  amounts	of  memory that are summed are not gathered atomically which also
       introduce an error in the result.

       The different values has the following relation to each other. Values  beginning  with  an
       uppercase letter is not part of the result.

	       total = processes + system
	       processes = processes_used + ProcessesNotUsed
	       system = atom + binary + code + ets + OtherSystem
	       atom = atom_used + AtomNotUsed

	       RealTotal = processes + RealSystem
	       RealSystem = system + MissedSystem

       More tuples in the returned list may be added in the future.

   Note:
       The  total value is supposed to be the total amount of memory dynamically allocated by the
       emulator. Shared libraries, the code of the emulator itself, and the emulator stack(s) are
       not  supposed  to be included. That is, the total value is not supposed to be equal to the
       total size of all pages mapped to the emulator. Furthermore, due to fragmentation and pre-
       reservation of memory areas, the size of the memory segments which contain the dynamically
       allocated memory blocks can be substantially larger than the total size of the dynamically
       allocated memory blocks.

   Note:
       Since erts version 5.6.4 erlang:memory/0 requires that all erts_alloc(3erl) allocators are
       enabled (default behaviour).

       Failure:

	 notsup :
	   If an erts_alloc(3erl) allocator has been disabled.

       erlang:memory(Type | [Type]) -> Size | [{Type, Size}]

	      Types  Type, Size -- see below

	      Returns the memory size in bytes allocated for memory of type Type .  The  argument
	      can  also  be  given as a list of Type atoms, in which case a corresponding list of
	      {Type, Size} tuples is returned.

   Note:
       Since erts version 5.6.4 erlang:memory/1 requires that all erts_alloc(3erl) allocators are
       enabled (default behaviour).

       Failures:

	 badarg :
	   If  Type is not one of the memory types listed in the documentation of erlang:memory/0
	   .

	 badarg :
	   If maximum is passed as Type and the emulator is not run in instrumented mode.

	 notsup :
	   If an erts_alloc(3erl) allocator has been disabled.

       See also erlang:memory/0 .

       min(Term1, Term2) -> Minimum

	      Types  Term1 = Term2 = Minimum = term()

	      Return the smallest of Term1 and Term2 ; if the terms compare equal, Term1 will  be
	      returned.

       module_loaded(Module) -> bool()

	      Types  Module = atom()

	      Returns  true if the module Module is loaded, otherwise returns false . It does not
	      attempt to load the module.

   Warning:
       This BIF is intended for the code server (see code(3erl) ) and should not  be  used  else-
       where.

       monitor(Type, Item) -> MonitorRef

	      Types  Type = process
		     Item = pid() | {RegName, Node} | RegName
		     RegName = atom()
		     Node = node()
		     MonitorRef = reference()

	      The calling process starts monitoring Item which is an object of type Type .

	      Currently  only processes can be monitored, i.e. the only allowed Type is process ,
	      but other types may be allowed in the future.

	      Item can be:

		pid() :
		  The pid of the process to monitor.

		{RegName, Node} :
		  A tuple consisting of a registered name of a	process  and  a  node  name.  The
		  process residing on the node Node with the registered name RegName will be mon-
		  itored.

		RegName :
		  The process locally registered as RegName will be monitored.

   Note:
       When a process is monitored by registered name, the process that has the  registered  name
       at  the time when monitor/2 is called will be monitored. The monitor will not be effected,
       if the registered name is unregistered.

       A 'DOWN' message will be sent to the monitoring process if Item dies,  if  Item	does  not
       exist,  or  if  the connection is lost to the node which Item resides on. A 'DOWN' message
       has the following pattern:

       {'DOWN', MonitorRef, Type, Object, Info}

       where MonitorRef and Type are the same as described above, and:

	 Object :
	   A reference to the monitored object:

	   * the pid of the monitored process, if Item was specified as a pid.

	   * {RegName, Node} , if Item was specified as {RegName, Node} .

	   * {RegName, Node} , if Item was specified as RegName . Node will in this case  be  the
	     name of the local node ( node() ).

	 Info :
	   Either  the exit reason of the process, noproc (non-existing process), or noconnection
	   (no connection to Node ).

   Note:
       If/when monitor/2 is extended (e.g. to handle other item types than process ), other  pos-
       sible values for Object , and Info in the 'DOWN' message will be introduced.

       The  monitoring	is turned off either when the 'DOWN' message is sent, or when demonitor/1
       is called.

       If an attempt is made to monitor a process on an older node (where remote process monitor-
       ing  is	not  implemented or one where remote process monitoring by registered name is not
       implemented), the call fails with badarg .

       Making several calls to monitor/2 for the same Item is not an  error;  it  results  in  as
       many, completely independent, monitorings.

   Note:
       The  format  of the 'DOWN' message changed in the 5.2 version of the emulator (OTP release
       R9B) for monitor by registered name . The Object element of the 'DOWN'  message	could  in
       earlier versions sometimes be the pid of the monitored process and sometimes be the regis-
       tered name. Now the Object element is always a tuple consisting of the registered name and
       the  node  name.  Processes on new nodes (emulator version 5.2 or greater) will always get
       'DOWN' messages on the new format even if they are monitoring processes on old nodes. Pro-
       cesses on old nodes will always get 'DOWN' messages on the old format.

       monitor_node(Node, Flag) -> true

	      Types  Node = node()
		     Flag = bool()

	      Monitors	the  status of the node Node . If Flag is true , monitoring is turned on;
	      if Flag is false , monitoring is turned off.

	      Making several calls to monitor_node(Node, true) for the same Node is not an error;
	      it results in as many, completely independent, monitorings.

	      If  Node	fails or does not exist, the message {nodedown, Node} is delivered to the
	      process. If a process has made two calls to monitor_node(Node, true) and Node  ter-
	      minates, two nodedown messages are delivered to the process. If there is no connec-
	      tion to Node , there will be an attempt to create one. If this  fails,  a  nodedown
	      message is delivered.

	      Nodes connected through hidden connections can be monitored as any other node.

	      Failure: badarg if the local node is not alive.

       erlang:monitor_node(Node, Flag, Options) -> true

	      Types  Node = node()
		     Flag = bool()
		     Options = [Option]
		     Option = allow_passive_connect

	      Behaves as monitor_node/2 except that it allows an extra option to be given, namely
	      allow_passive_connect . The option allows the BIF to wait the normal net connection
	      timeout  for  the  monitored  node to connect itself, even if it cannot be actively
	      connected from this node (i.e. it is blocked). The state where this might be useful
	      can  only  be  achieved by using the kernel option dist_auto_connect once . If that
	      kernel option is not used, the allow_passive_connect option has no effect.

   Note:
       The allow_passive_connect option is used internally and is seldom needed  in  applications
       where the network topology and the kernel options in effect is known in advance.

       Failure: badarg if the local node is not alive or the option list is malformed.

       erlang:nif_error(Reason)

	      Types  Reason = term()

	      Works  exactly  like erlang:error/1 , but Dialyzer thinks that this BIF will return
	      an arbitrary term. When used in a stub function for a NIF to generate an	exception
	      when the NIF library is not loaded, Dialyzer will not generate false warnings.

       erlang:nif_error(Reason, Args)

	      Types  Reason = term()
		     Args = [term()]

	      Works  exactly  like erlang:error/2 , but Dialyzer thinks that this BIF will return
	      an arbitrary term. When used in a stub function for a NIF to generate an	exception
	      when the NIF library is not loaded, Dialyzer will not generate false warnings.

       node() -> Node

	      Types  Node = node()

	      Returns  the  name  of  the  local node. If the node is not alive, nonode@nohost is
	      returned instead.

	      Allowed in guard tests.

       node(Arg) -> Node

	      Types  Arg = pid() | port() | reference()
		     Node = node()

	      Returns the node where Arg is located. Arg can be a pid, a reference, or a port. If
	      the local node is not alive, nonode@nohost is returned.

	      Allowed in guard tests.

       nodes() -> Nodes

	      Types  Nodes = [node()]

	      Returns  a  list of all visible nodes in the system, excluding the local node. Same
	      as nodes(visible) .

       nodes(Arg | [Arg]) -> Nodes

	      Types  Arg = visible | hidden | connected | this | known
		     Nodes = [node()]

	      Returns a list of nodes according to argument given. The result returned	when  the
	      argument	is a list, is the list of nodes satisfying the disjunction(s) of the list
	      elements.

	      Arg can be any of the following:

		visible :
		  Nodes connected to this node through normal connections.

		hidden :
		  Nodes connected to this node through hidden connections.

		connected :
		  All nodes connected to this node.

		this :
		  This node.

		known :
		  Nodes which are known to this node, i.e., connected, previously connected, etc.

	      Some equalities: [node()] = nodes(this) , nodes(connected) =  nodes([visible,  hid-
	      den]) , and nodes() = nodes(visible) .

	      If  the  local  node is not alive, nodes(this) == nodes(known) == [nonode@nohost] ,
	      for any other Arg the empty list [] is returned.

       now() -> {MegaSecs, Secs, MicroSecs}

	      Types  MegaSecs = Secs = MicroSecs = int()

	      Returns the tuple {MegaSecs, Secs, MicroSecs} which is the elapsed time since 00:00
	      GMT,  January 1, 1970 (zero hour) on the assumption that the underlying OS supports
	      this. Otherwise, some other point in time is chosen. It  is  also  guaranteed  that
	      subsequent  calls  to  this  BIF returns continuously increasing values. Hence, the
	      return value from now() can be used to generate unique time-stamps, and  if  it  is
	      called in a tight loop on a fast machine the time of the node can become skewed.

	      It  can  only  be  used to check the local time of day if the time-zone info of the
	      underlying operating system is properly configured.

       open_port(PortName, PortSettings) -> port()

	      Types  PortName = {spawn, Command} | {spawn_driver, Command}  |  {spawn_executable,
		     FileName} | {fd, In, Out}
		     Command = string()
		     FileName = [ FileNameChar ] | binary()
		     FileNameChar = int() (1..255 or any Unicode codepoint, see description)
		     In = Out = int()
		     PortSettings = [Opt]
		     Opt  =  {packet, N} | stream | {line, L} | {cd, Dir} | {env, Env} | {args, [
		     ArgString ]} | {arg0, ArgString} | exit_status | use_stdio |  nouse_stdio	|
		     stderr_to_stdout | in | out | binary | eof
		     N = 1 | 2 | 4
		     L = int()
		     Dir = string()
		     ArgString = [ FileNameChar ] | binary()
		     Env = [{Name, Val}]
		     Name = string()
		     Val = string() | false

	      Returns a port identifier as the result of opening a new Erlang port. A port can be
	      seen as an external Erlang process. PortName is one of the following:

		{spawn, Command} :
		  Starts an external program. Command is the name of the external  program  which
		  will be run. Command runs outside the Erlang work space unless an Erlang driver
		  with the name Command is found. If found, that driver will be started. A driver
		  runs	in  the  Erlang  workspace, which means that it is linked with the Erlang
		  runtime system.

		  When starting external programs on Solaris, the system call vfork  is  used  in
		  preference  to fork for performance reasons, although it has a history of being
		  less robust. If there are problems with using vfork , setting  the  environment
		  variable ERL_NO_VFORK to any value will cause fork to be used instead.

		  For external programs, the PATH is searched (or an equivalent method is used to
		  find programs, depending on operating system). This is  done	by  invoking  the
		  shell  och  certain  platforms.  The first space separated token of the command
		  will be considered as the name of the executable (or driver). This (among other
		  things) makes this option unsuitable for running programs having spaces in file
		  or directory names. Use {spawn_executable, Command} instead if spaces  in  exe-
		  cutable file names is desired.

		{spawn_driver, Command} :
		  Works  like {spawn, Command} , but demands the first (space separated) token of
		  the command to be the name of a loaded driver. If no driver with that  name  is
		  loaded, a badarg error is raised.

		{spawn_executable, Command} :
		  Works  like  {spawn, Command} , but only runs external executables. The Command
		  in its whole is used as the name of the executable, including  any  spaces.  If
		  arguments are to be passed, the args and arg0 PortSettings can be used.

		  The  shell is not usually invoked to start the program, it's executed directly.
		  Neither is the PATH (or equivalent) searched. To find a program in the PATH  to
		  execute, use os:find_executable/1 .

		  Only if a shell script or .bat file is executed, the appropriate command inter-
		  preter will implicitly be invoked, but there will still be no command  argument
		  expansion or implicit PATH search.

		  The  name  of the executable as well as the arguments given in args and arg0 is
		  subject to Unicode file name translation if the system is  running  in  Unicode
		  file name mode. To avoid translation or force i.e. UTF-8, supply the executable
		  and/or arguments as a binary in the correct encoding. See the file module,  the
		  file:native_name_encoding/0 function and the stdlib users guide for details.

   Note:The  characters  in  the  name (if given as a list) can only be > 255 if the Erlang VM is
       started in Unicode file name translation mode, otherwise the name  of  the  executable  is
       limited to the ISO-latin-1 character set.
	 If  the Command cannot be run, an error exception, with the posix error code as the rea-
	 son, is raised. The error reason may differ between  operating  systems.  Typically  the
	 error	enoent is raised when one tries to run a program that is not found and eaccess is
	 raised when the given file is not executable.

       {fd, In, Out} :
	 Allows an Erlang process to access any currently opened file descriptors used by Erlang.
	 The  file  descriptor In can be used for standard input, and the file descriptor Out for
	 standard output. It is only used for various servers in the Erlang  operating	system	(
	 shell and user ). Hence, its use is very limited.

       PortSettings is a list of settings for the port. Valid settings are:

	 {packet, N} :
	   Messages are preceded by their length, sent in N bytes, with the most significant byte
	   first. Valid values for N are 1, 2, or 4.

	 stream :
	   Output messages are sent without packet lengths. A user-defined protocol must be  used
	   between the Erlang process and the external object.

	 {line, L} :
	   Messages  are  delivered on a per line basis. Each line (delimited by the OS-dependent
	   newline sequence) is delivered in one single  message.  The	message  data  format  is
	   {Flag, Line} , where Flag is either eol or noeol and Line is the actual data delivered
	   (without the newline sequence).

	   L specifies the maximum line length in bytes. Lines longer than this will be delivered
	   in  more than one message, with the Flag set to noeol for all but the last message. If
	   end of file	is  encountered  anywhere  else  than  immediately  following  a  newline
	   sequence,  the  last  line  will also be delivered with the Flag set to noeol . In all
	   other cases, lines are delivered with Flag set to eol .

	   The {packet, N} and {line, L} settings are mutually exclusive.

	 {cd, Dir} :
	   This is only valid for {spawn, Command} and {spawn_executable, Command} . The external
	   program starts using Dir as its working directory. Dir must be a string. Not available
	   on VxWorks.

	 {env, Env} :
	   This is only valid for {spawn, Command} and {spawn_executable, Command} . The environ-
	   ment of the started process is extended using the environment specifications in Env .

	   Env	should be a list of tuples {Name, Val} , where Name is the name of an environment
	   variable, and Val is the value it is to have in the spawned port  process.  Both  Name
	   and	Val  must  be  strings. The one exception is Val being the atom false (in analogy
	   with os:getenv/1 ), which removes the environment variable. Not available on VxWorks.

	 {args, [ string() ]} :
	   This option is only valid for {spawn_executable, Command} and specifies  arguments  to
	   the	executable.  Each argument is given as a separate string and (on Unix) eventually
	   ends up as one element each in the argument vector. On other platforms, similar behav-
	   ior is mimicked.

	   The arguments are not expanded by the shell prior to being supplied to the executable,
	   most  notably  this	means  that  file  wildcard  expansion	will  not   happen.   Use
	   filelib:wildcard/1  to  expand wildcards for the arguments. Note that even if the pro-
	   gram is a Unix shell script, meaning that the shell will ultimately be invoked,  wild-
	   card  expansion  will  not  happen  and the script will be provided with the untouched
	   arguments. On Windows(R), wildcard expansion is always up to the program  itself,  why
	   this isn't an issue.

	   Note  also  that  the  actual executable name (a.k.a. argv[0] ) should not be given in
	   this list. The proper executable name will automatically  be  used  as  argv[0]  where
	   applicable.

	   When the Erlang VM is running in Unicode file name mode, the arguments can contain any
	   Unicode characters and will be translated into whatever is appropriate on the underly-
	   ing	OS,  which  means  UTF-8  for all platforms except Windows, which has other (more
	   transparent) ways of dealing with Unicode arguments	to  programs.  To  avoid  Unicode
	   translation	of  arguments,	they  can be supplied as binaries in whatever encoding is
	   deemed appropriate.

   Note:The characters in the arguments (if given as a list of characters) can only be >  255  if
       the Erlang VM is started in Unicode file name mode, otherwise the arguments are limited to
       the ISO-latin-1 character set.
	 If one, for any reason, wants to explicitly set the program name in the argument vector,
	 the arg0 option can be used.

       {arg0, string()} :
	 This  option  is only valid for {spawn_executable, Command} and explicitly specifies the
	 program name argument when running an executable. This might in some  circumstances,  on
	 some  operating systems, be desirable. How the program responds to this is highly system
	 dependent and no specific effect is guaranteed.

	 The unicode file name translation rules of the args option apply to this option as well.

       exit_status :
	 This is only valid for {spawn, Command} where Command refers to an external program, and
	 for {spawn_executable, Command} .

	 When  the  external  process  connected  to  the  port  exits,  a  message  of  the form
	 {Port,{exit_status,Status}} is sent to the connected process, where Status is	the  exit
	 status  of  the  external process. If the program aborts, on Unix the same convention is
	 used as the shells do (i.e., 128+signal).

	 If the eof option has been given as well, the eof message and	the  exit_status  message
	 appear in an unspecified order.

	 If  the  port program closes its stdout without exiting, the exit_status option will not
	 work.

       use_stdio :
	 This is only valid for {spawn, Command} and {spawn_executable, Command} . It allows  the
	 standard  input  and output (file descriptors 0 and 1) of the spawned (UNIX) process for
	 communication with Erlang.

       nouse_stdio :
	 The opposite of use_stdio . Uses file descriptors 3 and 4 for communication with Erlang.

       stderr_to_stdout :
	 Affects ports to external programs. The executed program gets its  standard  error  file
	 redirected  to  its  standard output file. stderr_to_stdout and nouse_stdio are mutually
	 exclusive.

       overlapped_io :
	 Affects ports to external programs on Windows(R) only. The standard input  and  standard
	 output  handles of the port program will, if this option is supplied, be opened with the
	 flag FILE_FLAG_OVERLAPPED, so that the port program can (and has to) do  overlapped  I/O
	 on  its standard handles. This is not normally the case for simple port programs, but an
	 option of value for the experienced Windows programmer. On  all  other  platforms,  this
	 option is silently discarded .

       in :
	 The port can only be used for input.

       out :
	 The port can only be used for output.

       binary :
	 All IO from the port are binary data objects as opposed to lists of bytes.

       eof :
	 The  port will not be closed at the end of the file and produce an exit signal. Instead,
	 it will remain open and a {Port, eof} message will be sent to the  process  holding  the
	 port.

       hide :
	 When  running	on  Windows,  suppress creation of a new console window when spawning the
	 port program. (This option has no effect on other platforms.)

       The default is stream for all types of port and use_stdio for spawned ports.

       Failure: If the port cannot be opened, the exit reason is badarg , system_limit ,  or  the
       Posix  error  code  which  most closely describes the error, or einval if no Posix code is
       appropriate:

	 badarg :
	   Bad input arguments to open_port .

	 system_limit :
	   All available ports in the Erlang emulator are in use.

	 enomem :
	   There was not enough memory to create the port.

	 eagain :
	   There are no more available operating system processes.

	 enametoolong :
	   The external command given was too long.

	 emfile :
	   There are no more available file descriptors (for the operating  system  process  that
	   the Erlang emulator runs in).

	 enfile :
	   The file table is full (for the entire operating system).

	 eacces :
	   The	Command  given	in  {spawn_executable,	Command} does not point out an executable
	   file.

	 enoent :
	   The Command given in {spawn_executable, Command} does not point out an existing file.

       During use of a port opened using {spawn, Name}	,  {spawn_driver,  Name}  or  {spawn_exe-
       cutable,  Name}	,  errors  arising when sending messages to it are reported to the owning
       process using signals of the form {'EXIT', Port, PosixCode} . See file(3erl) for  possible
       values of PosixCode .

       The  maximum number of ports that can be open at the same time is 1024 by default, but can
       be configured by the environment variable ERL_MAX_PORTS .

       erlang:phash(Term, Range) -> Hash

	      Types  Term = term()
		     Range = 1..2^32
		     Hash = 1..Range

	      Portable hash function that will give the  same  hash  for  the  same  Erlang  term
	      regardless of machine architecture and ERTS version (the BIF was introduced in ERTS
	      4.9.1.1). Range can be between 1 and 2^32, the function returns a  hash  value  for
	      Term within the range 1..Range .

	      This  BIF could be used instead of the old deprecated erlang:hash/2 BIF, as it cal-
	      culates better hashes for all data-types, but consider using phash2/1,2 instead.

       erlang:phash2(Term [, Range]) -> Hash

	      Types  Term = term()
		     Range = 1..2^32
		     Hash = 0..Range-1

	      Portable hash function that will give the  same  hash  for  the  same  Erlang  term
	      regardless of machine architecture and ERTS version (the BIF was introduced in ERTS
	      5.2). Range can be between 1 and 2^32, the function returns a hash value	for  Term
	      within  the  range  0..Range-1 . When called without the Range argument, a value in
	      the range 0..2^27-1 is returned.

	      This BIF should always be used for hashing terms.  It  distributes  small  integers
	      better than phash/2 , and it is faster for bignums and binaries.

	      Note that the range 0..Range-1 is different from the range of phash/2 ( 1..Range ).

       pid_to_list(Pid) -> string()

	      Types  Pid = pid()

	      Returns a string which corresponds to the text representation of Pid .

   Warning:
       This  BIF  is intended for debugging and for use in the Erlang operating system. It should
       not be used in application programs.

       port_close(Port) -> true

	      Types  Port = port() | atom()

	      Closes an open port. Roughly the same as Port !  {self(),  close}  except  for  the
	      error behaviour (see below), and that the port does not reply with {Port, closed} .
	      Any process may close a port with port_close/1 , not only the port owner (the  con-
	      nected process).

	      For  comparison: Port ! {self(), close} fails with badarg if Port cannot be sent to
	      (i.e., Port refers neither to a port nor to a process). If Port is  a  closed  port
	      nothing happens. If Port is an open port and the calling process is the port owner,
	      the port replies with {Port, closed} when all buffers have  been	flushed  and  the
	      port really closes, but if the calling process is not the port owner the port owner
	      fails with badsig .

	      Note that any process can close a port using Port ! {PortOwner, close} just  as  if
	      it itself was the port owner, but the reply always goes to the port owner.

	      In  short:  port_close(Port)  has  a cleaner and more logical behaviour than Port !
	      {self(), close} .

	      Failure: badarg if Port is not an open port or the registered name of an open port.

       port_command(Port, Data) -> true

	      Types  Port = port() | atom()
		     Data = iodata()

	      Sends data to a port. Same as Port ! {self(), {command, Data}} except for the error
	      behaviour  (see  below).	Any process may send data to a port with port_command/2 ,
	      not only the port owner (the connected process).

	      For comparison: Port ! {self(), {command, Data}} fails with badarg if  Port  cannot
	      be  sent	to  (i.e.,  Port refers neither to a port nor to a process). If Port is a
	      closed port the data message disappears without a sound. If Port is  open  and  the
	      calling  process is not the port owner, the port owner fails with badsig . The port
	      owner fails with badsig also if Data is not a valid IO list.

	      Note that any process can send to a port using Port ! {PortOwner, {command,  Data}}
	      just as if it itself was the port owner.

	      In  short:  port_command(Port,  Data) has a cleaner and more logical behaviour than
	      Port ! {self(), {command, Data}} .

	      If the port is busy, the calling process will be suspended until the  port  is  not
	      busy anymore.

	      Failures:

		badarg :
		  If Port is not an open port or the registered name of an open port.

		badarg :
		  If Data is not a valid io list.

       port_command(Port, Data, OptionList) -> true|false

	      Types  Port = port() | atom()
		     Data = iodata()
		     OptionList = [Option]
		     Option = force
		     Option = nosuspend

	      Sends  data to a port. port_command(Port, Data, []) equals port_command(Port, Data)
	      .

	      If the port command is aborted false is returned; otherwise, true is returned.

	      If the port is busy, the calling process will be suspended until the  port  is  not
	      busy anymore.

	      Currently the following Option s are valid:

		force :
		  The  calling	process  will  not be suspended if the port is busy; instead, the
		  port command is forced through. The call will fail with a notsup  exception  if
		  the  driver  of  the	port  does not support this. For more information see the
		  ERL_DRV_FLAG_SOFT_BUSY driver flag.

		nosuspend :
		  The calling process will not be suspended if the port  is  busy;  instead,  the
		  port command is aborted and false is returned.

   Note:
       More options may be added in the future.

       Failures:

	 badarg :
	   If Port is not an open port or the registered name of an open port.

	 badarg :
	   If Data is not a valid io list.

	 badarg :
	   If OptionList is not a valid option list.

	 notsup :
	   If the force option has been passed, but the driver of the port does not allow forcing
	   through a busy port.

       port_connect(Port, Pid) -> true

	      Types  Port = port() | atom()
		     Pid = pid()

	      Sets the port owner (the connected port) to Pid  .  Roughly  the	same  as  Port	!
	      {self(), {connect, Pid}} except for the following:

		* The error behavior differs, see below.

		* The port does not reply with {Port,connected} .

		* The new port owner gets linked to the port.

	      The  old	port owner stays linked to the port and have to call unlink(Port) if this
	      is not desired. Any process may set the port owner to be any process with port_con-
	      nect/2 .

	      For comparison: Port ! {self(), {connect, Pid}} fails with badarg if Port cannot be
	      sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed
	      port  nothing  happens. If Port is an open port and the calling process is the port
	      owner, the port replies with {Port, connected} to the old port owner. Note that the
	      old  port owner is still linked to the port, and that the new is not. If Port is an
	      open port and the calling process is not the port owner, the port owner fails  with
	      badsig . The port owner fails with badsig also if Pid is not an existing local pid.

	      Note  that  any  process	can set the port owner using Port ! {PortOwner, {connect,
	      Pid}} just as if it itself was the port owner, but the reply  always  goes  to  the
	      port owner.

	      In  short:  port_connect(Port,  Pid)  has a cleaner and more logical behaviour than
	      Port ! {self(),{connect,Pid}} .

	      Failure: badarg if Port is not an open port or the registered name of an open port,
	      or if Pid is not an existing local pid.

       port_control(Port, Operation, Data) -> Res

	      Types  Port = port() | atom()
		     Operation = int()
		     Data = Res = iodata()

	      Performs	a  synchronous	control operation on a port. The meaning of Operation and
	      Data depends on the port, i.e., on the port driver. Not all  port  drivers  support
	      this control feature.

	      Returns:	a  list of integers in the range 0 through 255, or a binary, depending on
	      the port driver. The meaning of the returned data also depends on the port driver.

	      Failure: badarg if Port is not an open port or the registered name of an open port,
	      if  Operation  cannot  fit in a 32-bit integer, if the port driver does not support
	      synchronous control operations, or if the port driver so	decides  for  any  reason
	      (probably something wrong with Operation or Data ).

       erlang:port_call(Port, Operation, Data) -> term()

	      Types  Port = port() | atom()
		     Operation = int()
		     Data = term()

	      Performs a synchronous call to a port. The meaning of Operation and Data depends on
	      the port, i.e., on the port driver. Not all port drivers support this feature.

	      Port is a port identifier, referring to a driver.

	      Operation is an integer, which is passed on to the driver.

	      Data is any Erlang term. This data is converted to binary term format and  sent  to
	      the port.

	      Returns:	a  term from the driver. The meaning of the returned data also depends on
	      the port driver.

	      Failure: badarg if Port is not an open port or the registered name of an open port,
	      if  Operation  cannot  fit in a 32-bit integer, if the port driver does not support
	      synchronous control operations, or if the port driver so	decides  for  any  reason
	      (probably something wrong with Operation or Data ).

       erlang:port_info(Port) -> [{Item, Info}] | undefined

	      Types  Port = port() | atom()
		     Item, Info -- see below

	      Returns  a list containing tuples with information about the Port , or undefined if
	      the port is not open. The order of the tuples is	not  defined,  nor  are  all  the
	      tuples mandatory.

		{registered_name, RegName} :
		  RegName (an atom) is the registered name of the port. If the port has no regis-
		  tered name, this tuple is not present in the list.

		{id, Index} :
		  Index (an integer) is the internal index of the port. This index may be used to
		  separate ports.

		{connected, Pid} :
		  Pid is the process connected to the port.

		{links, Pids} :
		  Pids is a list of pids to which processes the port is linked.

		{name, String} :
		  String is the command name set by open_port .

		{input, Bytes} :
		  Bytes is the total number of bytes read from the port.

		{output, Bytes} :
		  Bytes is the total number of bytes written to the port.

	      Failure: badarg if Port is not a local port.

       erlang:port_info(Port, Item) -> {Item, Info} | undefined | []

	      Types  Port = port() | atom()
		     Item, Info -- see below

	      Returns  information  about Port as specified by Item , or undefined if the port is
	      not open. Also, if Item == registered_name and the port has no registered name,  []
	      is returned.

	      For   valid   values   of   Item	 ,   and  corresponding  values  of  Info  ,  see
	      erlang:port_info/1 .

	      Failure: badarg if Port is not a local port.

       erlang:port_to_list(Port) -> string()

	      Types  Port = port()

	      Returns a string which corresponds to the text representation of the  port  identi-
	      fier Port .

   Warning:
       This  BIF  is intended for debugging and for use in the Erlang operating system. It should
       not be used in application programs.

       erlang:ports() -> [port()]

	      Returns a list of all ports on the local node.

       pre_loaded() -> [Module]

	      Types  Module = atom()

	      Returns a list of Erlang modules which are pre-loaded in the system. As all loading
	      of code is done through the file system, the file system must have been loaded pre-
	      viously. Hence, at least the module init must be pre-loaded.

       erlang:process_display(Pid, Type) -> void()

	      Types  Pid = pid()
		     Type = backtrace

	      Writes information about the local process Pid on  standard  error.  The	currently
	      allowed value for the atom Type is backtrace , which shows the contents of the call
	      stack, including information about  the  call  chain,  with  the	current  function
	      printed first. The format of the output is not further defined.

       process_flag(Flag, Value) -> OldValue

	      Types  Flag, Value, OldValue -- see below

	      Sets certain flags for the process which calls this function. Returns the old value
	      of the flag.

		process_flag(trap_exit, Boolean) :
		  When trap_exit is set to true , exit signals arriving to  a  process	are  con-
		  verted  to  {'EXIT',	From, Reason} messages, which can be received as ordinary
		  messages. If trap_exit is set to false , the process exits if  it  receives  an
		  exit	signal	other than normal and the exit signal is propagated to its linked
		  processes. Application processes should normally not trap exits.

		  See also exit/2 .

		process_flag(error_handler, Module) :
		  This is used by a process to redefine the error handler for undefined  function
		  calls  and  undefined  registered processes. Inexperienced users should not use
		  this flag since code auto-loading is dependent on the correct operation of  the
		  error handling module.

		process_flag(min_heap_size, MinHeapSize) :
		  This changes the minimum heap size for the calling process.

		process_flag(min_bin_vheap_size, MinBinVHeapSize) :
		  This changes the minimum binary virtual heap size for the calling process.

		process_flag(priority, Level) :
		  This sets the process priority. Level is an atom. There are currently four pri-
		  ority levels: low , normal , high , and max . The  default  priority	level  is
		  normal  .  NOTE  :  The  max priority level is reserved for internal use in the
		  Erlang runtime system, and should not be used by others.

		  Internally in each priority level processes are  scheduled  in  a  round  robin
		  fashion.

		  Execution of processes on priority normal and priority low will be interleaved.
		  Processes on priority low will be selected for execution less  frequently  than
		  processes on priority normal .

		  When there are runnable processes on priority high no processes on priority low
		  , or normal will be selected for execution. Note, however, that this	does  not
		  mean	that  no  processes  on priority low , or normal will be able to run when
		  there are processes on priority high running. On the runtime	system	with  SMP
		  support  there  might  be  more processes running in parallel than processes on
		  priority high , i.e., a low , and a high priority process might execute at  the
		  same time.

		  When	there are runnable processes on priority max no processes on priority low
		  , normal , or high will be selected for execution. As with the  high	priority,
		  processes  on lower priorities might execute in parallel with processes on pri-
		  ority max .

		  Scheduling is preemptive. Regardless of priority, a process is  preempted  when
		  it has consumed more than a certain amount of reductions since the last time it
		  was selected for execution.

		  NOTE : You should not depend on the scheduling  to  remain  exactly  as  it  is
		  today.  Scheduling,  at  least  on the runtime system with SMP support, is very
		  likely to be modified in the future in order to better utilize  available  pro-
		  cessor cores.

		  There is currently no automatic mechanism for avoiding priority inversion, such
		  as priority inheritance, or priority ceilings. When using priorities	you  have
		  to take this into account and handle such scenarios by yourself.

		  Making calls from a high priority process into code that you don't have control
		  over may cause the high priority process to wait for	a  processes  with  lower
		  priority,  i.e.,  effectively  decreasing  the  priority  of	the high priority
		  process during the call. Even if this isn't the case with one  version  of  the
		  code	that  you don't have under your control, it might be the case in a future
		  version of it. This might, for example, happen if a high priority process trig-
		  gers code loading, since the code server runs on priority normal .

		  Other priorities than normal are normally not needed. When other priorities are
		  used, they need to be used with care, especially the high priority must be used
		  with	care. A process on high priority should only perform work for short peri-
		  ods of time. Busy looping for long periods of time in a high	priority  process
		  will	most likely cause problems, since there are important servers in OTP run-
		  ning on priority normal .

		process_flag(save_calls, N) :
		  When there are runnable processes on priority max no processes on priority  low
		  ,  normal  , or high will be selected for execution. As with the high priority,
		  processes on lower priorities might execute in parallel with processes on  pri-
		  ority max .

		  N  must  be  an integer in the interval 0..10000. If N > 0, call saving is made
		  active for the process, which means that information about the  N  most  recent
		  global  function  calls,  BIF calls, sends and receives made by the process are
		  saved in a list, which can be retrieved with process_info(Pid, last_calls) .	A
		  global  function  call is one in which the module of the function is explicitly
		  mentioned. Only a fixed amount of information is saved: a tuple {Module,  Func-
		  tion,  Arity} for function calls, and the mere atoms send , 'receive' and time-
		  out for sends and receives ( 'receive' when a message is received  and  timeout
		  when	a  receive times out). If N = 0, call saving is disabled for the process,
		  which is the default. Whenever the size of the call saving  list  is	set,  its
		  contents are reset.

		process_flag(sensitive, Boolean) :
		  Set  or  clear  the  sensitive flag for the current process. When a process has
		  been marked as sensitive by calling process_flag(sensitive, true) , features in
		  the  run-time system that can be used for examining the data and/or inner work-
		  ing of the process are silently disabled.

		  Features that are disabled include (but are not limited to) the following:

		  Tracing: Trace flags can still be set for the process, but no trace messages of
		  any  kind  will  be generated. (If the sensitive flag is turned off, trace mes-
		  sages will again be generated if there are any trace flags set.)

		  Sequential tracing: The sequential trace token will be propagated as usual, but
		  no sequential trace messages will be generated.

		  process_info/1,2  cannot  be	used to read out the message queue or the process
		  dictionary (both will be returned as empty lists).

		  Stack back-traces cannot be displayed for the process.

		  In crash dumps, the stack, messages, and the process dictionary will	be  omit-
		  ted.

		  If {save_calls,N} has been set for the process, no function calls will be saved
		  to the call saving list. (The call saving list will not  be  cleared;  further-
		  more, send, receive, and timeout events will still be added to the list.)

       process_flag(Pid, Flag, Value) -> OldValue

	      Types  Pid = pid()
		     Flag, Value, OldValue -- see below

	      Sets  certain  flags  for  the process Pid , in the same manner as process_flag/2 .
	      Returns the old value of the flag. The allowed values for Flag are only a subset of
	      those allowed in process_flag/2 , namely: save_calls .

	      Failure: badarg if Pid is not a local process.

       process_info(Pid) -> InfoResult

	      Types  Pid = pid()
		     Item = atom()
		     Info = term()
		     InfoTuple = {Item, Info}
		     InfoTupleList = [InfoTuple]
		     InfoResult = InfoTupleList | undefined

	      Returns  a  list	containing  InfoTuple  s with miscellaneous information about the
	      process identified by Pid , or undefined if the process is not alive.

	      The order of the InfoTuple s is not defined, nor are all the InfoTuple s mandatory.
	      The  InfoTuple  s part of the result may be changed without prior notice. Currently
	      InfoTuple s with the following Item s are part of the  result:  current_function	,
	      initial_call  ,  status  ,  message_queue_len  ,	messages  ,  links , dictionary ,
	      trap_exit , error_handler , priority , group_leader , total_heap_size , heap_size ,
	      stack_size , reductions , and garbage_collection . If the process identified by Pid
	      has a registered name also an InfoTuple with Item == registered_name will appear.

	      See process_info/2 for information about specific InfoTuple s.

   Warning:
       This BIF is intended for debugging only , use process_info/2 for all other purposes.

       Failure: badarg if Pid is not a local process.

       process_info(Pid, ItemSpec) -> InfoResult

	      Types  Pid = pid()
		     Item = atom()
		     Info = term()
		     ItemList = [Item]
		     ItemSpec = Item | ItemList
		     InfoTuple = {Item, Info}
		     InfoTupleList = [InfoTuple]
		     InfoResult = InfoTuple | InfoTupleList | undefined | []

	      Returns information about the process identified by Pid as specified by  the  Item-
	      Spec , or undefined if the process is not alive.

	      If  the  process is alive and ItemSpec is a single Item , the returned value is the
	      corresponding InfoTuple unless ItemSpec == registered_name and the process  has  no
	      registered  name. In this case [] is returned. This strange behavior is due to his-
	      torical reasons, and is kept for backward compatibility.

	      If ItemSpec is an ItemList , the result is an InfoTupleList . The  InfoTuple  s  in
	      the  InfoTupleList  will	appear with the corresponding Item s in the same order as
	      the Item s appeared in the ItemList . Valid Item s may appear multiple times in the
	      ItemList .

   Note:
       If registered_name is part of an ItemList and the process has no name registered a {regis-
       tered_name, []} InfoTuple will appear in the resulting InfoTupleList .  This  behavior  is
       different than when ItemSpec == registered_name , and than when process_info/1 is used.

       Currently the following InfoTuple s with corresponding Item s are valid:

	 {backtrace, Bin} :
	   The	binary	Bin  contains the same information as the output from erlang:process_dis-
	   play(Pid, backtrace) . Use binary_to_list/1 to obtain the string  of  characters  from
	   the binary.

	 {binary, BinInfo} :
	   BinInfo  is a list containing miscellaneous information about binaries currently being
	   referred to by this process. This InfoTuple may be changed or  removed  without  prior
	   notice.

	 {catchlevel, CatchLevel} :
	   CatchLevel  is  the number of currently active catches in this process. This InfoTuple
	   may be changed or removed without prior notice.

	 {current_function, {Module, Function, Args}} :
	   Module , Function , Args is the current function call of the process.

	 {dictionary, Dictionary} :
	   Dictionary is the dictionary of the process.

	 {error_handler, Module} :
	   Module is the error handler module used by the process (for undefined function  calls,
	   for example).

	 {garbage_collection, GCInfo} :
	   GCInfo is a list which contains miscellaneous information about garbage collection for
	   this process. The content of GCInfo may be changed without prior notice.

	 {group_leader, GroupLeader} :
	   GroupLeader is group leader for the IO of the process.

	 {heap_size, Size} :
	   Size is the size in words of youngest heap generation of the process. This  generation
	   currently  include the stack of the process. This information is highly implementation
	   dependent, and may change if the implementation change.

	 {initial_call, {Module, Function, Arity}} :
	   Module , Function , Arity is the initial function call  with  which	the  process  was
	   spawned.

	 {links, Pids} :
	   Pids is a list of pids, with processes to which the process has a link.

	 {last_calls, false|Calls} :
	   The value is false if call saving is not active for the process (see process_flag/3 ).
	   If call saving is active, a list is returned, in which the last element  is	the  most
	   recent called.

	 {memory, Size} :
	   Size  is the size in bytes of the process. This includes call stack, heap and internal
	   structures.

	 {message_binary, BinInfo} :
	   BinInfo is a list containing miscellaneous information about binaries currently  being
	   referred to by the message area. This InfoTuple is only valid on an emulator using the
	   hybrid heap type. This InfoTuple may be changed or removed without prior notice.

	 {message_queue_len, MessageQueueLen} :
	   MessageQueueLen is the number of messages  currently  in  the  message  queue  of  the
	   process.  This  is  the length of the list MessageQueue returned as the info item mes-
	   sages (see below).

	 {messages, MessageQueue} :
	   MessageQueue is a list of the messages to the process, which have not  yet  been  pro-
	   cessed.

	 {min_heap_size, MinHeapSize} :
	   MinHeapSize is the minimum heap size for the process.

	 {min_bin_vheap_size, MinBinVHeapSize} :
	   MinBinVHeapSize is the minimum binary virtual heap size for the process.

	 {monitored_by, Pids} :
	   A list of pids that are monitoring the process (with monitor/2 ).

	 {monitors, Monitors} :
	   A  list  of	monitors  (started  by monitor/2 ) that are active for the process. For a
	   local process monitor or a remote process monitor by pid, the list item  is	{process,
	   Pid}  , and for a remote process monitor by name, the list item is {process, {RegName,
	   Node}} .

	 {priority, Level} :
	   Level is the current priority level for the process. For more information  on  priori-
	   ties see process_flag(priority, Level) .

	 {reductions, Number} :
	   Number is the number of reductions executed by the process.

	 {registered_name, Atom} :
	   Atom  is  the  registered  name of the process. If the process has no registered name,
	   this tuple is not present in the list.

	 {sequential_trace_token, [] | SequentialTraceToken} :
	   SequentialTraceToken the sequential trace token for the process. This InfoTuple may be
	   changed or removed without prior notice.

	 {stack_size, Size} :
	   Size is the stack size of the process in words.

	 {status, Status} :
	   Status  is the status of the process. Status is exiting , garbage_collecting , waiting
	   (for a message), running , runnable (ready to run, but another process is running), or
	   suspended (suspended on a "busy" port or by the erlang:suspend_process/[1,2] BIF).

	 {suspending, SuspendeeList} :
	   SuspendeeList  is  a  list of {Suspendee, ActiveSuspendCount, OutstandingSuspendCount}
	   tuples. Suspendee is the pid of a process that have been or is to be suspended by  the
	   process  identified	by  Pid  via the erlang:suspend_process/2 BIF, or the erlang:sus-
	   pend_process/1 BIF. ActiveSuspendCount is the number of times the Suspendee	has  been
	   suspended  by Pid . OutstandingSuspendCount is the number of not yet completed suspend
	   requests sent by Pid . That is, if ActiveSuspendCount /= 0 , Suspendee is currently in
	   the	suspended  state,  and if OutstandingSuspendCount /= 0 the asynchronous option of
	   erlang:suspend_process/2 has been used and the suspendee has not yet been suspended by
	   Pid	.  Note that the ActiveSuspendCount and OutstandingSuspendCount are not the total
	   suspend count on Suspendee , only the parts contributed by Pid .

	 {total_heap_size, Size} :
	   Size is the total size in words of all heap fragments of the process.  This	currently
	   include the stack of the process.

	 {trace, InternalTraceFlags} :
	   InternalTraceFlags  is  an  integer representing internal trace flag for this process.
	   This InfoTuple may be changed or removed without prior notice.

	 {trap_exit, Boolean} :
	   Boolean is true if the process is trapping exits, otherwise it is false .

       Note however, that not all implementations support every one of the above Items .

       Failure: badarg if Pid is not a local process, or if Item is not a valid Item .

       processes() -> [pid()]

	      Returns a list of process identifiers corresponding to all the processes	currently
	      existing on the local node.

	      Note   that   a	process   that	is  exiting,  exists  but  is  not  alive,  i.e.,
	      is_process_alive/1 will return false for a process that is exiting, but its process
	      identifier will be part of the result returned from processes/0 .

	      > processes().
	      [<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]

       purge_module(Module) -> void()

	      Types  Module = atom()

	      Removes  old code for Module . Before this BIF is used, erlang:check_process_code/2
	      should be called to check that no processes are executing old code in the module.

   Warning:
       This BIF is intended for the code server (see code(3erl) ) and should not  be  used  else-
       where.

       Failure: badarg if there is no old code for Module .

       put(Key, Val) -> OldVal | undefined

	      Types  Key = Val = OldVal = term()

	      Adds  a  new  Key  to  the  process dictionary, associated with the value Val , and
	      returns undefined . If Key already exists, the old value is deleted and replaced by
	      Val and the function returns the old value.

   Note:
       The  values stored when put is evaluated within the scope of a catch will not be retracted
       if a throw is evaluated, or if an error occurs.

       > X = put(name, walrus), Y = put(name, carpenter),
       Z = get(name),
       {X, Y, Z}.
       {undefined,walrus,carpenter}

       erlang:raise(Class, Reason, Stacktrace)

	      Types  Class = error | exit | throw
		     Reason = term()
		     Stacktrace = [{Module, Function, Arity | Args} | {Fun, Args}]
		     Module = Function = atom()
		     Arity = int()
		     Args = [term()]
		     Fun = [fun()]

	      Stops the execution of the calling process with an exception of given class, reason
	      and call stack backtrace ( stacktrace ).

   Warning:
       This BIF is intended for debugging and for use in the Erlang operating system. In general,
       it should be avoided in applications, unless you know very well what you are doing.

       Class is one of	error  ,  exit	or  throw  ,  so  if  it  were	not  for  the  stacktrace
       erlang:raise(Class,  Reason, Stacktrace) is equivalent to erlang:Class(Reason) . Reason is
       any term and Stacktrace is a list as returned from get_stacktrace() , that is  a  list  of
       3-tuples  {Module,  Function,  Arity  |	Args} where Module and Function are atoms and the
       third element is an integer arity or an argument list. The  stacktrace  may  also  contain
       {Fun, Args} tuples where Fun is a local fun and Args is an argument list.

       The  stacktrace	is  used  as the exception stacktrace for the calling process; it will be
       truncated to the current maximum stacktrace depth.

       Because evaluating this function causes the process to terminate, it has no return value -
       unless  the  arguments  are invalid, in which case the function returns the error reason ,
       that  is  badarg  .  If	you  want  to  be  really  sure  not  to  return  you  can   call
       error(erlang:raise(Class, Reason, Stacktrace)) and hope to distinguish exceptions later.

       erlang:read_timer(TimerRef) -> int() | false

	      Types  TimerRef = reference()

	      TimerRef	  is	a    timer   reference	 returned   by	 erlang:send_after/3   or
	      erlang:start_timer/3 . If the timer is active, the function  returns  the  time  in
	      milliseconds  left  until  the timer will expire, otherwise false (which means that
	      TimerRef was never a timer, that it has been cancelled,  or  that  it  has  already
	      delivered its message).

	      See also erlang:send_after/3 , erlang:start_timer/3 , and erlang:cancel_timer/1 .

       erlang:ref_to_list(Ref) -> string()

	      Types  Ref = reference()

	      Returns a string which corresponds to the text representation of Ref .

   Warning:
       This  BIF  is intended for debugging and for use in the Erlang operating system. It should
       not be used in application programs.

       register(RegName, Pid | Port) -> true

	      Types  RegName = atom()
		     Pid = pid()
		     Port = port()

	      Associates the name RegName with a pid or a port identifier. RegName ,  which  must
	      be an atom, can be used instead of the pid / port identifier in the send operator (
	      RegName ! Message ).

	      > register(db, Pid).
	      true

	      Failure: badarg if Pid is not an existing, local process or  port,  if  RegName  is
	      already  in use, if the process or port is already registered (already has a name),
	      or if RegName is the atom undefined .

       registered() -> [RegName]

	      Types  RegName = atom()

	      Returns a list of names which have been registered using register/2 .

	      > registered().
	      [code_server, file_server, init, user, my_db]

       erlang:resume_process(Suspendee) -> true

	      Types  Suspendee = pid()

	      Decreases the suspend count on the process  identified  by  Suspendee  .	Suspendee
	      should previously have been suspended via erlang:suspend_process/2 , or erlang:sus-
	      pend_process/1 by the process calling erlang:resume_process(Suspendee) .	When  the
	      suspend  count  on Suspendee reach zero, Suspendee will be resumed, i.e., the state
	      of the Suspendee is changed from suspended into the state Suspendee was  in  before
	      it was suspended.

   Warning:
       This BIF is intended for debugging only.

       Failures:

	 badarg :
	   If Suspendee isn't a process identifier.

	 badarg :
	   If  the  process calling erlang:resume_process/1 had not previously increased the sus-
	   pend count on the process identified by Suspendee .

	 badarg :
	   If the process identified by Suspendee is not alive.

       round(Number) -> int()

	      Types  Number = number()

	      Returns an integer by rounding Number .

	      > round(5.5).
	      6

	      Allowed in guard tests.

       self() -> pid()

	      Returns the pid (process identifier) of the calling process.

	      > self().
	      <0.26.0>

	      Allowed in guard tests.

       erlang:send(Dest, Msg) -> Msg

	      Types  Dest = pid() | port() | RegName | {RegName, Node}
		     Msg = term()
		     RegName = atom()
		     Node = node()

	      Sends a message and returns Msg . This is the same as Dest ! Msg .

	      Dest may be a remote or local pid, a (local) port, a locally registered name, or	a
	      tuple {RegName, Node} for a registered name at another node.

       erlang:send(Dest, Msg, [Option]) -> Res

	      Types  Dest = pid() | port() | RegName | {RegName, Node}
		     RegName = atom()
		     Node = node()
		     Msg = term()
		     Option = nosuspend | noconnect
		     Res = ok | nosuspend | noconnect

	      Sends a message and returns ok , or does not send the message but returns something
	      else (see below). Otherwise the same as erlang:send/2 . See also erlang:send_nosus-
	      pend/2,3 . for more detailed explanation and warnings.

	      The possible options are:

		nosuspend :
		  If  the sender would have to be suspended to do the send, nosuspend is returned
		  instead.

		noconnect :
		  If the destination node would have to be auto-connected before doing the  send,
		  noconnect is returned instead.

   Warning:
       As with erlang:send_nosuspend/2,3 : Use with extreme care!

       erlang:send_after(Time, Dest, Msg) -> TimerRef

	      Types  Time = int()
		     0 <= Time <= 4294967295
		     Dest = pid() | RegName
		     LocalPid = pid() (of a process, alive or dead, on the local node)
		     Msg = term()
		     TimerRef = reference()

	      Starts a timer which will send the message Msg to Dest after Time milliseconds.

	      If  Dest	is  an	atom,  it is supposed to be the name of a registered process. The
	      process referred to by the name is looked up at the time of delivery. No	error  is
	      given if the name does not refer to a process.

	      If  Dest is a pid, the timer will be automatically canceled if the process referred
	      to by the pid is not alive, or when the process exits. This feature was  introduced
	      in  erts	version  5.4.11. Note that timers will not be automatically canceled when
	      Dest is an atom.

	      See also erlang:start_timer/3 , erlang:cancel_timer/1 , and erlang:read_timer/1 .

	      Failure: badarg if the arguments does not satisfy the requirements specified above.

       erlang:send_nosuspend(Dest, Msg) -> bool()

	      Types  Dest = pid() | port() | RegName | {RegName, Node}
		     RegName = atom()
		     Node = node()
		     Msg = term()

	      The same as erlang:send(Dest, Msg, [nosuspend]) , but returns true if  the  message
	      was sent and false if the message was not sent because the sender would have had to
	      be suspended.

	      This function is intended for send operations towards  an  unreliable  remote  node
	      without ever blocking the sending (Erlang) process. If the connection to the remote
	      node (usually not a real Erlang node, but a node written in C  or  Java)	is  over-
	      loaded, this function will not send the message but return false instead.

	      The same happens, if Dest refers to a local port that is busy. For all other desti-
	      nations (allowed for the ordinary send operator '!' ) this function sends the  mes-
	      sage and returns true .

	      This  function is only to be used in very rare circumstances where a process commu-
	      nicates with Erlang nodes that can disappear without any trace causing the TCP buf-
	      fers  and  the  drivers queue to be over-full before the node will actually be shut
	      down (due to tick timeouts) by net_kernel . The normal reaction to take  when  this
	      happens is some kind of premature shutdown of the other node.

	      Note  that  ignoring the return value from this function would result in unreliable
	      message passing, which is contradictory to the Erlang programming model.	The  mes-
	      sage is not sent if this function returns false .

	      Note  also  that in many systems, transient states of overloaded queues are normal.
	      The fact that this function returns false does not in any way mean that  the  other
	      node  is	guaranteed to be non-responsive, it could be a temporary overload. Also a
	      return value of true does only mean that the message could be  sent  on  the  (TCP)
	      channel  without	blocking,  the	message  is not guaranteed to have arrived at the
	      remote node. Also in the case of a disconnected  non-responsive  node,  the  return
	      value  is  true (mimics the behaviour of the ! operator). The expected behaviour as
	      well as the actions to take when the function returns  false  are  application  and
	      hardware specific.

   Warning:
       Use with extreme care!

       erlang:send_nosuspend(Dest, Msg, Options) -> bool()

	      Types  Dest = pid() | port() | RegName | {RegName, Node}
		     RegName = atom()
		     Node = node()
		     Msg = term()
		     Option = noconnect

	      The same as erlang:send(Dest, Msg, [nosuspend | Options]) , but with boolean return
	      value.

	      This function behaves like erlang:send_nosuspend/2) , but takes a third  parameter,
	      a  list of options. The only currently implemented option is noconnect . The option
	      noconnect makes the function return false if  the  remote  node  is  not	currently
	      reachable by the local node. The normal behaviour is to try to connect to the node,
	      which may stall the process for a shorter period. The use of the	noconnect  option
	      makes  it  possible  to be absolutely sure not to get even the slightest delay when
	      sending to a remote process. This is  especially	useful	when  communicating  with
	      nodes  who  expect  to  always  be  the connecting part (i.e. nodes written in C or
	      Java).

	      Whenever the function returns false (either when a  suspend  would  occur  or  when
	      noconnect  was  specified  and  the node was not already connected), the message is
	      guaranteed not to have been sent.

   Warning:
       Use with extreme care!

       erlang:set_cookie(Node, Cookie) -> true

	      Types  Node = node()
		     Cookie = atom()

	      Sets the magic cookie of Node to the atom Cookie . If Node is the local  node,  the
	      function also sets the cookie of all other unknown nodes to Cookie (see Distributed
	      Erlang in the Erlang Reference Manual).

	      Failure: function_clause if the local node is not alive.

       setelement(Index, Tuple1, Value) -> Tuple2

	      Types  Index = 1..tuple_size(Tuple1)
		     Tuple1 = Tuple2 = tuple()
		     Value = term()

	      Returns a tuple which is a copy of the argument Tuple1 with the  element	given  by
	      the integer argument Index (the first element is the element with index 1) replaced
	      by the argument Value .

	      > setelement(2, {10, green, bottles}, red).
	      {10,red,bottles}

       size(Item) -> int()

	      Types  Item = tuple() | binary()

	      Returns an integer which is the size of the argument Item , which must be either	a
	      tuple or a binary.

	      > size({morni, mulle, bwange}).
	      3

	      Allowed in guard tests.

       spawn(Fun) -> pid()

	      Types  Fun = fun()

	      Returns  the  pid  of  a new process started by the application of Fun to the empty
	      list [] . Otherwise works like spawn/3 .

       spawn(Node, Fun) -> pid()

	      Types  Node = node()
		     Fun = fun()

	      Returns the pid of a new process started by the application of  Fun  to  the  empty
	      list  []	on  Node  .  If Node does not exist, a useless pid is returned. Otherwise
	      works like spawn/3 .

       spawn(Module, Function, Args) -> pid()

	      Types  Module = Function = atom()
		     Args = [term()]

	      Returns the pid of a new process started by the application of  Module:Function  to
	      Args  . The new process created will be placed in the system scheduler queue and be
	      run some time later.

	      error_handler:undefined_function(Module, Function, Args) is evaluated  by  the  new
	      process  if Module:Function/Arity does not exist (where Arity is the length of Args
	      ). The error handler can be redefined (see process_flag/2 ).  If	error_handler  is
	      undefined,  or  the user has redefined the default error_handler its replacement is
	      undefined, a failure with the reason undef will occur.

	      > spawn(speed, regulator, [high_speed, thin_cut]).
	      <0.13.1>

       spawn(Node, Module, Function, Args) -> pid()

	      Types  Node = node()
		     Module = Function = atom()
		     Args = [term()]

	      Returns the pid of a new process started by the application of  Module:Function  to
	      Args  on Node . If Node does not exists, a useless pid is returned. Otherwise works
	      like spawn/3 .

       spawn_link(Fun) -> pid()

	      Types  Fun = fun()

	      Returns the pid of a new process started by the application of  Fun  to  the  empty
	      list  []. A link is created between the calling process and the new process, atomi-
	      cally. Otherwise works like spawn/3 .

       spawn_link(Node, Fun) -> pid()

	      Types  Node = node()
		     Fun = fun()

	      Returns the pid of a new process started by the application of  Fun  to  the  empty
	      list  []	on  Node  .  A	link  is  created between the calling process and the new
	      process, atomically. If Node does not exist, a useless pid is returned (and due  to
	      the link, an exit signal with exit reason noconnection will be received). Otherwise
	      works like spawn/3 .

       spawn_link(Module, Function, Args) -> pid()

	      Types  Module = Function = atom()
		     Args = [term()]

	      Returns the pid of a new process started by the application of  Module:Function  to
	      Args  .  A  link is created between the calling process and the new process, atomi-
	      cally. Otherwise works like spawn/3 .

       spawn_link(Node, Module, Function, Args) -> pid()

	      Types  Node = node()
		     Module = Function = atom()
		     Args = [term()]

	      Returns the pid of a new process started by the application of  Module:Function  to
	      Args  on	Node . A link is created between the calling process and the new process,
	      atomically. If Node does not exist, a useless pid is returned (and due to the link,
	      an  exit	signal	with  exit reason noconnection will be received). Otherwise works
	      like spawn/3 .

       spawn_monitor(Fun) -> {pid(),reference()}

	      Types  Fun = fun()

	      Returns the pid of a new process started by the application of  Fun  to  the  empty
	      list  []	and  reference	for a monitor created to the new process. Otherwise works
	      like spawn/3 .

       spawn_monitor(Module, Function, Args) -> {pid(),reference()}

	      Types  Module = Function = atom()
		     Args = [term()]

	      A new process is started by the application of Module:Function to Args  ,  and  the
	      process is monitored at the same time. Returns the pid and a reference for the mon-
	      itor. Otherwise works like spawn/3 .

       spawn_opt(Fun, [Option]) -> pid() | {pid(),reference()}

	      Types  Fun = fun()
		     Option = link | monitor | {priority, Level} |  {fullsweep_after,  Number}	|
		     {min_heap_size, Size} | {min_bin_vheap_size, VSize}
		     Level = low | normal | high
		     Number = int()
		     Size = int()
		     VSize = int()

	      Returns  the  pid  of  a new process started by the application of Fun to the empty
	      list [] . Otherwise works like spawn_opt/4 .

	      If the option monitor is given, the newly created process  will  be  monitored  and
	      both the pid and reference for the monitor will be returned.

       spawn_opt(Node, Fun, [Option]) -> pid()

	      Types  Node = node()
		     Fun = fun()
		     Option   =   link	 |   {priority,  Level}  |  {fullsweep_after,  Number}	|
		     {min_heap_size, Size} | {min_bin_vheap_size, VSize}
		     Level = low | normal | high
		     Number = int()
		     Size = int()
		     VSize = int()

	      Returns the pid of a new process started by the application of  Fun  to  the  empty
	      list  []	on  Node  .  If Node does not exist, a useless pid is returned. Otherwise
	      works like spawn_opt/4 .

       spawn_opt(Module, Function, Args, [Option]) -> pid() | {pid(),reference()}

	      Types  Module = Function = atom()
		     Args = [term()]
		     Option = link | monitor | {priority, Level} |  {fullsweep_after,  Number}	|
		     {min_heap_size, Size} | {min_bin_vheap_size, VSize}
		     Level = low | normal | high
		     Number = int()
		     Size = int()
		     VSize = int()

	      Works  exactly like spawn/3 , except that an extra option list is given when creat-
	      ing the process.

	      If the option monitor is given, the newly created process  will  be  monitored  and
	      both the pid and reference for the monitor will be returned.

		link :
		  Sets a link to the parent process (like spawn_link/3 does).

		monitor :
		  Monitor the new process (just like monitor/2 does).

		{priority, Level} :
		  Sets the priority of the new process. Equivalent to executing process_flag(pri-
		  ority, Level) in the start function of the new process, except that the  prior-
		  ity  will  be  set  before  the process is selected for execution for the first
		  time. For more information on priorities see process_flag(priority, Level) .

		{fullsweep_after, Number} :
		  This option is only useful for performance tuning. In general, you  should  not
		  use  this  option  unless  you  know that there is problem with execution times
		  and/or memory consumption, and you should measure to make sure that the  option
		  improved matters.

		  The  Erlang runtime system uses a generational garbage collection scheme, using
		  an "old heap" for data that has survived at least one garbage collection.  When
		  there  is  no more room on the old heap, a fullsweep garbage collection will be
		  done.

		  The fullsweep_after option makes it possible to specify the maximum  number  of
		  generational collections before forcing a fullsweep even if there is still room
		  on the old heap. Setting the number to zero effectively  disables  the  general
		  collection  algorithm,  meaning  that  all live data is copied at every garbage
		  collection.

		  Here are a few cases when it	could  be  useful  to  change  fullsweep_after	.
		  Firstly,  if	binaries that are no longer used should be thrown away as soon as
		  possible. (Set Number to zero.) Secondly, a process  that  mostly  have  short-
		  lived  data will be fullsweeped seldom or never, meaning that the old heap will
		  contain mostly garbage. To ensure a fullsweep once in a while, set Number to	a
		  suitable  value  such  as  10  or 20. Thirdly, in embedded systems with limited
		  amount of RAM and no virtual memory, one might want to preserve memory by  set-
		  ting	Number	to zero. (The value may be set globally, see erlang:system_flag/2
		  .)

		{min_heap_size, Size} :
		  This option is only useful for performance tuning. In general, you  should  not
		  use  this  option  unless  you  know that there is problem with execution times
		  and/or memory consumption, and you should measure to make sure that the  option
		  improved matters.

		  Gives  a  minimum heap size in words. Setting this value higher than the system
		  default might speed up some processes because less garbage collection is  done.
		  Setting  too	high  value, however, might waste memory and slow down the system
		  due to worse data locality. Therefore, it is recommended  to	use  this  option
		  only for fine-tuning an application and to measure the execution time with var-
		  ious Size values.

		{min_bin_vheap_size, VSize} :
		  This option is only useful for performance tuning. In general, you  should  not
		  use  this  option  unless  you  know that there is problem with execution times
		  and/or memory consumption, and you should measure to make sure that the  option
		  improved matters.

		  Gives  a  minimum  binary virtual heap size in words. Setting this value higher
		  than the system default might speed up some processes because less garbage col-
		  lection  is  done.  Setting too high value, however, might waste memory. There-
		  fore, it is recommended to use this option only for fine-tuning an  application
		  and to measure the execution time with various VSize values.

       spawn_opt(Node, Module, Function, Args, [Option]) -> pid()

	      Types  Node = node()
		     Module = Function = atom()
		     Args = [term()]
		     Option   =   link	 |   {priority,  Level}  |  {fullsweep_after,  Number}	|
		     {min_heap_size, Size} | {min_bin_vheap_size, VSize}
		     Level = low | normal | high
		     Number = int()
		     Size = int()
		     VSize = int()

	      Returns the pid of a new process started by the application of  Module:Function  to
	      Args  on	Node . If Node does not exist, a useless pid is returned. Otherwise works
	      like spawn_opt/4 .

       split_binary(Bin, Pos) -> {Bin1, Bin2}

	      Types  Bin = Bin1 = Bin2 = binary()
		     Pos = 0..byte_size(Bin)

	      Returns a tuple containing the binaries which are the result of splitting Bin  into
	      two  parts  at position Pos . This is not a destructive operation. After the opera-
	      tion, there will be three binaries altogether.

	      > B = list_to_binary("0123456789").
	      <<"0123456789">>
	      > byte_size(B).
	      10
	      > {B1, B2} = split_binary(B,3).
	      {<<"012">>,<<"3456789">>}
	      > byte_size(B1).
	      3
	      > byte_size(B2).
	      7

       erlang:start_timer(Time, Dest, Msg) -> TimerRef

	      Types  Time = int()
		     0 <= Time <= 4294967295
		     Dest = LocalPid | RegName
		     LocalPid = pid() (of a process, alive or dead, on the local node)
		     RegName = atom()
		     Msg = term()
		     TimerRef = reference()

	      Starts a timer which will send the message {timeout, TimerRef, Msg} to  Dest  after
	      Time milliseconds.

	      If  Dest	is  an	atom,  it is supposed to be the name of a registered process. The
	      process referred to by the name is looked up at the time of delivery. No	error  is
	      given if the name does not refer to a process.

	      If  Dest is a pid, the timer will be automatically canceled if the process referred
	      to by the pid is not alive, or when the process exits. This feature was  introduced
	      in  erts	version  5.4.11. Note that timers will not be automatically canceled when
	      Dest is an atom.

	      See also erlang:send_after/3 , erlang:cancel_timer/1 , and erlang:read_timer/1 .

	      Failure: badarg if the arguments does not satisfy the requirements specified above.

       statistics(Type) -> Res

	      Types  Type, Res -- see below

	      Returns information about the system as specified by Type :

		context_switches :
		  Returns {ContextSwitches, 0} , where ContextSwitches is  the	total  number  of
		  context switches since the system started.

		exact_reductions :
		  Returns {Total_Exact_Reductions, Exact_Reductions_Since_Last_Call} .

		  NOTE:  statistics(exact_reductions)  is a more expensive operation than statis-
		  tics(reductions) especially on an Erlang machine with SMP support.

		garbage_collection :
		  Returns {Number_of_GCs, Words_Reclaimed, 0} . This information may not be valid
		  for all implementations.

		io :
		  Returns {{input, Input}, {output, Output}} , where Input is the total number of
		  bytes received through ports, and Output is the total number of bytes output to
		  ports.

		reductions :
		  Returns {Total_Reductions, Reductions_Since_Last_Call} .

		  NOTE:  From  erts  version  5.5  (OTP release R11B) this value does not include
		  reductions performed in current time slices of currently  scheduled  processes.
		  If an exact value is wanted, use statistics(exact_reductions) .

		run_queue :
		  Returns  the length of the run queue, that is, the number of processes that are
		  ready to run.

		runtime :
		  Returns {Total_Run_Time, Time_Since_Last_Call} . Note that the run-time is  the
		  sum  of  the	run-time  for  all  threads in the Erlang run-time system and may
		  therefore be greater than the wall-clock time.

		wall_clock :
		  Returns {Total_Wallclock_Time, Wallclock_Time_Since_Last_Call} . wall_clock can
		  be  used  in	the same manner as runtime , except that real time is measured as
		  opposed to runtime or CPU time.

	      All times are in milliseconds.

	      > statistics(runtime).
	      {1690,1620}
	      > statistics(reductions).
	      {2046,11}
	      > statistics(garbage_collection).
	      {85,23961,0}

       erlang:suspend_process(Suspendee, OptList) -> true | false

	      Types  Suspendee = pid()
		     OptList = [Opt]
		     Opt = atom()

	      Increases the suspend count on the process identified by Suspendee and puts  it  in
	      the suspended state if it isn't already in the suspended state. A suspended process
	      will not be scheduled for execution until the process has been resumed.

	      A process can be suspended by multiple processes	and  can  be  suspended  multiple
	      times  by  a single process. A suspended process will not leave the suspended state
	      until its suspend count reach zero. The suspend count  of  Suspendee  is	decreased
	      when  erlang:resume_process(Suspendee)  is  called  by the same process that called
	      erlang:suspend_process(Suspendee) . All increased suspend counts on other processes
	      acquired by a process will automatically be decreased when the process terminates.

	      Currently the following options ( Opt s) are available:

		asynchronous :
		  A  suspend  request  is sent to the process identified by Suspendee . Suspendee
		  will eventually suspend unless it is resumed before it was able to suspend. The
		  caller  of  erlang:suspend_process/2	will  return  immediately,  regardless of
		  whether the Suspendee has suspended yet or not. Note that  the  point  in  time
		  when the Suspendee will actually suspend cannot be deduced from other events in
		  the system. The only guarantee given is that the Suspendee will eventually sus-
		  pend	(unless  it  is resumed). If the asynchronous option has not been passed,
		  the caller of erlang:suspend_process/2 will be blocked until the Suspendee  has
		  actually suspended.

		unless_suspending :
		  The  process	identified  by	Suspendee  will  be  suspended unless the calling
		  process already is suspending the Suspendee . If unless_suspending is  combined
		  with the asynchronous option, a suspend request will be sent unless the calling
		  process already is suspending the Suspendee or if a suspend request already has
		  been	sent  and is in transit. If the calling process already is suspending the
		  Suspendee , or if combined with the asynchronous  option  and  a  send  request
		  already  is  in  transit,  false is returned and the suspend count on Suspendee
		  will remain unchanged.

	      If the suspend count on the process identified by Suspendee was increased, true  is
	      returned; otherwise, false is returned.

   Warning:
       This BIF is intended for debugging only.

       Failures:

	 badarg :
	   If Suspendee isn't a process identifier.

	 badarg :
	   If  the  process  identified  by  Suspendee is same the process as the process calling
	   erlang:suspend_process/2 .

	 badarg :
	   If the process identified by Suspendee is not alive.

	 badarg :
	   If the process identified by Suspendee resides on another node.

	 badarg :
	   If OptList isn't a proper list of valid Opt s.

	 system_limit :
	   If the process identified by Suspendee has been suspended more times  by  the  calling
	   process  than  can  be represented by the currently used internal data structures. The
	   current system limit is larger than 2 000 000 000 suspends, and it will never be  less
	   than that.

       erlang:suspend_process(Suspendee) -> true

	      Types  Suspendee = pid()

	      Suspends	the  process  identified  by  Suspendee . The same as calling erlang:sus-
	      pend_process(Suspendee, [])  .  For  more  information  see  the	documentation  of
	      erlang:suspend_process/2 .

   Warning:
       This BIF is intended for debugging only.

       erlang:system_flag(Flag, Value) -> OldValue

	      Types  Flag, Value, OldValue -- see below

	      Sets  various  system  properties  of the Erlang node. Returns the old value of the
	      flag.

		erlang:system_flag(backtrace_depth, Depth) :
		  Sets the maximum depth of call stack back-traces in the exit reason element  of
		  'EXIT' tuples.

		erlang:system_flag(cpu_topology, CpuTopology) :
		  Sets the user defined CpuTopology . The user defined CPU topology will override
		  any automatically detected CPU topology. By passing  undefined  as  CpuTopology
		  the  system  will  revert  back to the CPU topology automatically detected. The
		  returned value equals the value returned from  erlang:system_info(cpu_topology)
		  before the change was made.

		  The  CPU  topology  is  used	when binding schedulers to logical processors. If
		  schedulers are already bound when the CPU topology is changed,  the  schedulers
		  will be sent a request to rebind according to the new CPU topology.

		  The  user defined CPU topology can also be set by passing the +sct command line
		  argument to erl .

		  For information on the CpuTopology type and  more,  see  the	documentation  of
		  erlang:system_info(cpu_topology)  , the erl +sct emulator flag, and erlang:sys-
		  tem_flag(scheduler_bind_type, How) .

		erlang:system_flag(fullsweep_after, Number) :
		  Number is a non-negative integer which indicates how	many  times  generational
		  garbage  collections	can  be  done without forcing a fullsweep collection. The
		  value applies to new processes; processes already running are not affected.

		  In low-memory systems (especially without virtual memory), setting the value to
		  0 can help to conserve memory.

		  An alternative way to set this value is through the (operating system) environ-
		  ment variable ERL_FULLSWEEP_AFTER .

		erlang:system_flag(min_heap_size, MinHeapSize) :
		  Sets the default minimum heap size for processes. The size is given  in  words.
		  The  new  min_heap_size  only  effects  processes  spawned  after the change of
		  min_heap_size has been made. The min_heap_size can be set for  individual  pro-
		  cesses by use of spawn_opt/N or process_flag/2 .

		erlang:system_flag(min_bin_vheap_size, MinBinVHeapSize) :
		  Sets	the  default  minimum binary virtual heap size for processes. The size is
		  given in words. The new  min_bin_vhheap_size	only  effects  processes  spawned
		  after  the  change of min_bin_vhheap_size has been made. The min_bin_vheap_size
		  can be set for individual processes by use of spawn_opt/N or process_flag/2 .

		erlang:system_flag(multi_scheduling, BlockState) :
		  BlockState = block | unblock

		  If multi-scheduling is enabled, more than one scheduler thread is used  by  the
		  emulator.  Multi-scheduling  can  be	blocked.  When	multi-scheduling has been
		  blocked, only one scheduler thread will schedule Erlang processes.

		  If BlockState =:= block , multi-scheduling will be blocked. If  BlockState  =:=
		  unblock  and no-one else is blocking multi-scheduling and this process has only
		  blocked one time, multi-scheduling will be unblocked.  One  process  can  block
		  multi-scheduling  multiple  times.  If a process has blocked multiple times, it
		  has to unblock exactly as many times as it has blocked before it  has  released
		  its  multi-scheduling  block.  If  a	process that has blocked multi-scheduling
		  exits, it will release its blocking of multi-scheduling.

		  The return values are disabled , blocked , or  enabled  .  The  returned  value
		  describes the state just after the call to erlang:system_flag(multi_scheduling,
		  BlockState) has been made. The return values are described in the documentation
		  of erlang:system_info(multi_scheduling) .

		  NOTE	: Blocking of multi-scheduling should normally not be needed. If you feel
		  that you need to block multi-scheduling, think through the problem at  least	a
		  couple  of times again. Blocking multi-scheduling should only be used as a last
		  resort since it will most likely be a very inefficient way to solve  the  prob-
		  lem.

		  See also erlang:system_info(multi_scheduling) , erlang:system_info(multi_sched-
		  uling_blockers) , and erlang:system_info(schedulers) .

		erlang:system_flag(scheduler_bind_type, How) :
		  Controls if and how schedulers are bound to logical processors.

		  When erlang:system_flag(scheduler_bind_type, How) is	called,  an  asynchronous
		  signal  is  sent  to	all schedulers online which causes them to try to bind or
		  unbind as requested. NOTE: If a scheduler fails to bind,  this  will	often  be
		  silently  ignored.  This since it isn't always possible to verify valid logical
		  processor identifiers. If an error is reported, it  will  be	reported  to  the
		  error_logger . If you want to verify that the schedulers actually have bound as
		  requested, call erlang:system_info(scheduler_bindings) .

		  Schedulers can currently only be bound on newer Linux,  Solaris,  FreeBSD,  and
		  Windows systems, but more systems will be supported in the future.

		  In order for the runtime system to be able to bind schedulers, the CPU topology
		  needs to be known. If the runtime system fails to automatically detect the  CPU
		  topology,  it  can  be  defined.  For more information on how to define the CPU
		  topology, see erlang:system_flag(cpu_topology, CpuTopology) .

		  The runtime system will by default bind schedulers to logical processors  using
		  the  default_bind  bind  type if the amount of schedulers are at least equal to
		  the amount of logical processors configured,	binding  of  schedulers  is  sup-
		  ported, and a CPU topology is available at startup.

		  NOTE:  If  the  Erlang runtime system is the only operating system process that
		  binds threads to logical processors, this improves the performance of the  run-
		  time	system.  However,  if  other  operating  system processes (as for example
		  another Erlang runtime system) also bind threads to logical  processors,  there
		  might  be  a	performance  penalty  instead.	If  this is the case you, are are
		  advised to unbind the schedulers using the  +sbtu  command  line  argument,  or
		  erlang:system_flag(scheduler_bind_type, unbound) .

		  Schedulers  can  be  bound  in  different ways. The How argument determines how
		  schedulers are bound. How can currently be one of:

		  unbound :
		    Schedulers will not be bound to logical processors, i.e., the operating  sys-
		    tem  decides  where  the scheduler threads execute, and when to migrate them.
		    This is the default.

		  no_spread :
		    Schedulers with close scheduler identifiers will be bound as close as  possi-
		    ble in hardware.

		  thread_spread :
		    Thread  refers  to	hardware  threads (e.g. Intels hyper-threads). Schedulers
		    with low scheduler identifiers, will be bound to the first hardware thread of
		    each core, then schedulers with higher scheduler identifiers will be bound to
		    the second hardware thread of each core, etc.

		  processor_spread :
		    Schedulers will be spread like thread_spread , but also over physical proces-
		    sor chips.

		  spread :
		    Schedulers will be spread as much as possible.

		  no_node_thread_spread :
		    Like  thread_spread  , but if multiple NUMA (Non-Uniform Memory Access) nodes
		    exists, schedulers will be spread over one NUMA node at  a	time,  i.e.,  all
		    logical processors of one NUMA node will be bound to schedulers in sequence.

		  no_node_processor_spread :
		    Like processor_spread , but if multiple NUMA nodes exists, schedulers will be
		    spread over one NUMA node at a time, i.e., all logical processors of one NUMA
		    node will be bound to schedulers in sequence.

		  thread_no_node_processor_spread :
		    A  combination  of	thread_spread , and no_node_processor_spread . Schedulers
		    will be spread over hardware threads across NUMA nodes, but  schedulers  will
		    only be spread over processors internally in one NUMA node at a time.

		  default_bind :
		    Binds    schedulers    the	  default   way.   Currently   the   default   is
		    thread_no_node_processor_spread (which might change in the future).

		  How schedulers are bound matters. For example, in  situations  when  there  are
		  fewer  running  processes  than  schedulers online, the runtime system tries to
		  migrate processes to schedulers with low scheduler identifiers.  The	more  the
		  schedulers  are  spread over the hardware, the more resources will be available
		  to the runtime system in such situations.

		  The value returned equals How before the scheduler_bind_type flag was changed.

		  Failure:

		  notsup :
		    If binding of schedulers is not supported.

		  badarg :
		    If How isn't one of the documented alternatives.

		  badarg :
		    If no CPU topology information is available.

		  The scheduler bind type can also be set by passing the +sbt command line  argu-
		  ment to erl .

		  For more information, see erlang:system_info(scheduler_bind_type) , erlang:sys-
		  tem_info(scheduler_bindings) , the erl  +sbt	emulator  flag,  and  erlang:sys-
		  tem_flag(cpu_topology, CpuTopology) .

		erlang:system_flag(schedulers_online, SchedulersOnline) :
		  Sets	the  amount  of  schedulers  online.  Valid  range is 1 <= SchedulerId <=
		  erlang:system_info(schedulers).

		  For more information	see,  erlang:system_info(schedulers)  ,  and  erlang:sys-
		  tem_info(schedulers_online) .

		erlang:system_flag(trace_control_word, TCW) :
		  Sets	the  value  of	the  node's  trace control word to TCW . TCW should be an
		  unsigned integer. For more information see documentation of the  set_tcw  func-
		  tion in the match specification documentation in the ERTS User's Guide.

   Note:
       The  schedulers	option has been removed as of erts version 5.5.3. The number of scheduler
       threads is determined at emulator boot time, and cannot be changed after that.

       erlang:system_info(Type) -> Res

	      Types  Type, Res -- see below

	      Returns various information about the current system  (emulator)	as  specified  by
	      Type :

		allocated_areas :
		  Returns  a list of tuples with information about miscellaneous allocated memory
		  areas.

		  Each tuple contains an atom describing type of  memory  as  first  element  and
		  amount  of  allocated  memory  in  bytes as second element. In those cases when
		  there is information present about allocated and used memory, a  third  element
		  is present. This third element contains the amount of used memory in bytes.

		  erlang:system_info(allocated_areas)  is intended for debugging, and the content
		  is highly implementation dependent. The content of the results  will	therefore
		  change when needed without prior notice.

		  Note:  The  sum  of these values is not the total amount of memory allocated by
		  the emulator. Some values are part of other values, and some memory  areas  are
		  not  part  of  the  result. If you are interested in the total amount of memory
		  allocated by the emulator see erlang:memory/0,1 .

		allocator :
		  Returns {Allocator, Version, Features, Settings}.

		  Types:

		  * Allocator = undefined | glibc

		  * Version = [int()]

		  * Features = [atom()]

		  * Settings = [{Subsystem, [{Parameter, Value}]}]

		  * Subsystem = atom()

		  * Parameter = atom()

		  * Value = term()

		  Explanation:

		  * Allocator corresponds to  the  malloc()  implementation  used.  If	Allocator
		    equals  undefined , the malloc() implementation used could not be identified.
		    Currently glibc can be identified.

		  * Version is a list of integers (but not a string) representing the version  of
		    the malloc() implementation used.

		  * Features is a list of atoms representing allocation features used.

		  * Settings  is  a  list  of subsystems, their configurable parameters, and used
		    values. Settings may differ  between  different  combinations  of  platforms,
		    allocators, and allocation features. Memory sizes are given in bytes.

		  See also "System Flags Effecting erts_alloc" in erts_alloc(3erl) .

		alloc_util_allocators :
		  Returns  a  list  of	the  names  of	all  allocators  using	the ERTS internal
		  alloc_util framework as atoms. For more information  see  the  "the  alloc_util
		  framework" section in the erts_alloc(3erl) documentation.

		{allocator, Alloc} :
		  Returns information about the specified allocator. As of erts version 5.6.1 the
		  return value is a list of {instance,	InstanceNo,  InstanceInfo}  tuples  where
		  InstanceInfo	contains  information about a specific instance of the allocator.
		  If Alloc is not a recognized allocator, undefined is returned. If Alloc is dis-
		  abled, false is returned.

		  Note:  The  information  returned is highly implementation dependent and may be
		  changed, or removed at any time without prior notice. It was initially intended
		  as a tool when developing new allocators, but since it might be of interest for
		  others it has been briefly documented.

		  The recognized allocators are listed in erts_alloc(3erl) .  After  reading  the
		  erts_alloc(3erl)  documentation,  the  returned information should more or less
		  speak for itself. But it can be worth explaining some things. Call  counts  are
		  presented by two values. The first value is giga calls, and the second value is
		  calls. mbcs , and sbcs are abbreviations for, respectively, multi-block  carri-
		  ers,	and single-block carriers. Sizes are presented in bytes. When it is not a
		  size that is presented, it is the amount of something. Sizes	and  amounts  are
		  often presented by three values, the first is current value, the second is max-
		  imum value since the last call to erlang:system_info({allocator, Alloc}) ,  and
		  the third is maximum value since the emulator was started. If only one value is
		  present, it is the current value. fix_alloc memory block types are presented by
		  two  values. The first value is memory pool size and the second value used mem-
		  ory size.

		{allocator_sizes, Alloc} :
		  Returns various size information for the specified allocator.  The  information
		  returned is a subset of the information returned by erlang:system_info({alloca-
		  tor, Alloc}) .

		build_type :
		  Returns an atom describing the build type of the runtime system. This  is  nor-
		  mally  the  atom  opt  for  optimized. Other possible return values are debug ,
		  purify , quantify , purecov , gcov , valgrind , gprof ,  and	lcnt  .  Possible
		  return values may be added and/or removed at any time without prior notice.

		c_compiler_used :
		  Returns  a  two-tuple describing the C compiler used when compiling the runtime
		  system. The first element is an atom describing the name of  the  compiler,  or
		  undefined  if  unknown.  The second element is a term describing the version of
		  the compiler, or undefined if unknown.

		check_io :
		  Returns a list containing miscellaneous  information	regarding  the	emulators
		  internal  I/O checking. Note, the content of the returned list may vary between
		  platforms and over time. The only thing guaranteed is that a list is returned.

		compat_rel :
		  Returns the compatibility mode of the local node as  an  integer.  The  integer
		  returned  represents the Erlang/OTP release which the current emulator has been
		  set to be backward compatible with. The compatibility mode can be configured at
		  startup by using the command line flag +R , see erl(1) .

		cpu_topology :
		  Returns the CpuTopology which currently is used by the emulator. The CPU topol-
		  ogy is used when binding schedulers to logical  processors.  The  CPU  topology
		  used	is  the user defined CPU topology if such exist; otherwise, the automati-
		  cally detected CPU topology if such exist. If no CPU topology  exist	undefined
		  is returned.

		  Types:

		  * CpuTopology = LevelEntryList | undefined

		  * LevelEntryList = [LevelEntry] (all LevelEntry s of a LevelEntryList must con-
		    tain the same LevelTag , except on the top level where both node and  proces-
		    sor LevelTag s may co-exist)

		  * LevelEntry	=  {LevelTag,  SubLevel} | {LevelTag, InfoList, SubLevel} ( {Lev-
		    elTag, SubLevel} == {LevelTag, [], SubLevel} )

		  * LevelTag = node|processor|core|thread (more LevelTag s may be  introduced  in
		    the future)

		  * SubLevel = [LevelEntry] | LogicalCpuId

		  * LogicalCpuId = {logical, integer()}

		  * InfoList = [] (the InfoList may be extended in the future)

		  node	refers	to  NUMA  (non-uniform memory access) nodes, and thread refers to
		  hardware threads (e.g. Intels hyper-threads).

		  A level in the CpuTopology term can be omitted if only one entry exists and the
		  InfoList is empty.

		  thread can only be a sub level to core . core can be a sub level to either pro-
		  cessor or node . processor can either be on the top level or	a  sub	level  to
		  node	.  node can either be on the top level or a sub level to processor . That
		  is, NUMA nodes can be processor internal or processor external. A CPU  topology
		  can  consist of a mix of processor internal and external NUMA nodes, as long as
		  each logical CPU belongs to one and only one NUMA node. Cache hierarchy is  not
		  part	of  the CpuTopology type yet, but will be in the future. Other things may
		  also make it into the CPU topology in the future. In other  words,  expect  the
		  CpuTopology type to change.

		{cpu_topology, defined} :
		  Returns  the user defined CpuTopology . For more information see the documenta-
		  tion of erlang:system_flag(cpu_topology, CpuTopology) and the documentation  of
		  the cpu_topology argument.

		{cpu_topology, detected} :
		  Returns  the	automatically  detected CpuTopology . The emulator currently only
		  detects the CPU topology on some newer Linux,  Solaris,  FreeBSD,  and  Windows
		  systems.  On Windows system with more than 32 logical processors the CPU topol-
		  ogy is not detected.

		  For more information see the documentation of the cpu_topology argument.

		{cpu_topology, used} :
		  Returns the CpuTopology which is used by the emulator. For more information see
		  the documentation of the cpu_topology argument.

		creation :
		  Returns  the	creation of the local node as an integer. The creation is changed
		  when a node is restarted. The creation of a node is stored in  process  identi-
		  fiers,  port identifiers, and references. This makes it (to some extent) possi-
		  ble to distinguish between identifiers from different incarnations of  a  node.
		  Currently  valid creations are integers in the range 1..3, but this may (proba-
		  bly will) change in the future. If the node is not alive, 0 is returned.

		debug_compiled :
		  Returns true if the emulator has been debug compiled; otherwise, false .

		dist :
		  Returns a binary containing a string of distribution information  formatted  as
		  in  Erlang  crash  dumps.  For  more	information see the "How to interpret the
		  Erlang crash dumps" chapter in the ERTS User's Guide.

		dist_ctrl :
		  Returns a list of tuples {Node, ControllingEntity} , one entry  for  each  con-
		  nected  remote node. The Node is the name of the node and the ControllingEntity
		  is the port or pid responsible for the communication to that node. More specif-
		  ically,  the ControllingEntity for nodes connected via TCP/IP (the normal case)
		  is the socket actually used in communication with the specific node.

		driver_version :
		  Returns a string containing the erlang driver version used by the runtime  sys-
		  tem. It will be on the form "<major ver>.<minor ver>" .

		elib_malloc :
		  This	option	will be removed in a future release. The return value will always
		  be false since the elib_malloc allocator has been removed.

		dist_buf_busy_limit :
		  Returns the value of the distribution buffer busy limit in  bytes.  This  limit
		  can be set on startup by passing the +zdbbl command line flag to erl .

		fullsweep_after :
		  Returns  {fullsweep_after,  int()} which is the fullsweep_after garbage collec-
		  tion setting used by	default.  For  more  information  see  garbage_collection
		  described below.

		garbage_collection :
		  Returns  a  list  describing the default garbage collection settings. A process
		  spawned on the local node by a spawn or spawn_link will use these garbage  col-
		  lection settings. The default settings can be changed by use of system_flag/2 .
		  spawn_opt/4 can spawn a process that does not use the default settings.

		global_heaps_size :
		  Returns the current size of the shared (global) heap.

		heap_sizes :
		  Returns a list of integers representing valid heap sizes in words.  All  Erlang
		  heaps are sized from sizes in this list.

		heap_type :
		  Returns  the	heap  type  used by the current emulator. Currently the following
		  heap types exist:

		  private :
		    Each process has a heap reserved for its use and no references between  heaps
		    of	different  processes  are  allowed. Messages passed between processes are
		    copied between heaps.

		  shared :
		    One heap for use by all processes.	Messages  passed  between  processes  are
		    passed by reference.

		  hybrid :
		    A  hybrid of the private and shared heap types. A shared heap as well as pri-
		    vate heaps are used.

		info :
		  Returns a binary containing a string of miscellaneous system	information  for-
		  matted as in Erlang crash dumps. For more information see the "How to interpret
		  the Erlang crash dumps" chapter in the ERTS User's Guide.

		kernel_poll :
		  Returns true if the emulator uses some kind of kernel-poll implementation; oth-
		  erwise, false .

		loaded :
		  Returns  a binary containing a string of loaded module information formatted as
		  in Erlang crash dumps. For more information  see  the  "How  to  interpret  the
		  Erlang crash dumps" chapter in the ERTS User's Guide.

		logical_processors :
		  Returns the detected number of logical processors configured on the system. The
		  return value is either an integer, or the atom unknown if the  emulator  wasn't
		  able to detect logical processors configured.

		logical_processors_available :
		  Returns  the detected number of logical processors available to the Erlang run-
		  time system. The return value is either an integer, or the atom unknown if  the
		  emulator wasn't able to detect logical processors available. The number of log-
		  ical processors available is less than or equal to the number of  logical  pro-
		  cessors online .

		logical_processors_online :
		  Returns  the	detected  number  of logical processors online on the system. The
		  return value is either an integer, or the atom unknown if the  emulator  wasn't
		  able	to  detect  logical  processors  online. The number of logical processors
		  online is less than or equal to the number of logical processors configured .

		machine :
		  Returns a string containing the Erlang machine name.

		min_heap_size :
		  Returns {min_heap_size, MinHeapSize} where MinHeapSize is  the  current  system
		  wide minimum heap size for spawned processes.

		min_bin_vheap_size :
		  Returns {min_bin_vheap_size, MinBinVHeapSize} where MinBinVHeapSize is the cur-
		  rent system wide minimum binary virtual heap size for spawned processes.

		modified_timing_level :
		  Returns the modified timing level (an integer)  if  modified	timing	has  been
		  enabled;  otherwise, undefined . See the +T command line flag in the documenta-
		  tion of the erl(1) command for more information on modified timing.

		multi_scheduling :
		  Returns disabled , blocked , or enabled . A description of the return values:

		  disabled :
		    The emulator has only one scheduler thread. The emulator does  not	have  SMP
		    support, or have been started with only one scheduler thread.

		  blocked :
		    The  emulator  has	more than one scheduler thread, but all scheduler threads
		    but one have been blocked, i.e., only  one	scheduler  thread  will  schedule
		    Erlang processes and execute Erlang code.

		  enabled :
		    The  emulator  has	more  than one scheduler thread, and no scheduler threads
		    have been blocked, i.e., all available scheduler threads will schedule Erlang
		    processes and execute Erlang code.

		  See	also   erlang:system_flag(multi_scheduling,   BlockState)  ,  erlang:sys-
		  tem_info(multi_scheduling_blockers) , and erlang:system_info(schedulers) .

		multi_scheduling_blockers :
		  Returns a list of PID s when multi-scheduling is blocked; otherwise, the  empty
		  list. The PID s in the list is PID s of the processes currently blocking multi-
		  scheduling. A PID will only be present once in the list,  even  if  the  corre-
		  sponding process has blocked multiple times.

		  See	also   erlang:system_flag(multi_scheduling,   BlockState)  ,  erlang:sys-
		  tem_info(multi_scheduling) , and erlang:system_info(schedulers) .

		otp_release :
		  Returns a string containing the OTP release number.

		process_count :
		  Returns the number of processes currently existing at  the  local  node  as  an
		  integer. The same value as length(processes()) returns.

		process_limit :
		  Returns the maximum number of concurrently existing processes at the local node
		  as an integer. This limit can be configured at startup  by  using  the  command
		  line flag +P , see erl(1) .

		procs :
		  Returns  a binary containing a string of process and port information formatted
		  as in Erlang crash dumps. For more information see the "How  to  interpret  the
		  Erlang crash dumps" chapter in the ERTS User's Guide.

		scheduler_bind_type :
		  Returns  information	on  how  user has requested schedulers to be bound or not
		  bound.

		  NOTE: Even though user has requested schedulers to  be  bound  via  erlang:sys-
		  tem_flag(scheduler_bind_type,  How)  , they might have silently failed to bind.
		  In order to inspect actual scheduler	bindings  call	erlang:system_info(sched-
		  uler_bindings) .

		  For  more  information,  see erlang:system_flag(scheduler_bind_type, How) , and
		  erlang:system_info(scheduler_bindings) .

		scheduler_bindings :
		  Returns information on currently used scheduler bindings.

		  A tuple of a size equal to erlang:system_info(schedulers) is returned. The ele-
		  ments of the tuple are integers or the atom unbound . Logical processor identi-
		  fiers are represented as integers. The N th element of  the  tuple  equals  the
		  current  binding  for  the scheduler with the scheduler identifier equal to N .
		  E.g., if the	schedulers  have  been	bound,	element(erlang:system_info(sched-
		  uler_id), erlang:system_info(scheduler_bindings)) will return the identifier of
		  the logical processor that the calling process is executing on.

		  Note that only schedulers online can be bound to logical processors.

		  For  more  information,  see	erlang:system_flag(scheduler_bind_type,  How)	,
		  erlang:system_info(schedulers_online) .

		scheduler_id :
		  Returns the scheduler id ( SchedulerId ) of the scheduler thread that the call-
		  ing process is executing on. SchedulerId is a  positive  integer;  where  1  <=
		  SchedulerId	<=   erlang:system_info(schedulers)   .   See	also  erlang:sys-
		  tem_info(schedulers) .

		schedulers :
		  Returns the number of scheduler threads used by the emulator. Scheduler threads
		  online schedules Erlang processes and Erlang ports, and execute Erlang code and
		  Erlang linked in driver code.

		  The number of scheduler threads is determined at emulator boot time and  cannot
		  be  changed  after that. The amount of schedulers online can however be changed
		  at any time.

		  See also erlang:system_flag(schedulers_online, SchedulersOnline) ,  erlang:sys-
		  tem_info(schedulers_online)  ,  erlang:system_info(scheduler_id)  , erlang:sys-
		  tem_flag(multi_scheduling, BlockState) , erlang:system_info(multi_scheduling) ,
		  and and erlang:system_info(multi_scheduling_blockers) .

		schedulers_online :
		  Returns  the	amount	of schedulers online. The scheduler identifiers of sched-
		  ulers  online  satisfy  the  following  relationship:  1  <=	 SchedulerId   <=
		  erlang:system_info(schedulers_online) .

		  For  more  information,  see	erlang:system_info(schedulers)	, and erlang:sys-
		  tem_flag(schedulers_online, SchedulersOnline) .

		smp_support :
		  Returns true if the emulator has been compiled  with	smp  support;  otherwise,
		  false .

		system_version :
		  Returns  a  string containing version number and some important properties such
		  as the number of schedulers.

		system_architecture :
		  Returns a string containing the processor and OS architecture the  emulator  is
		  built for.

		threads :
		  Returns  true if the emulator has been compiled with thread support; otherwise,
		  false is returned.

		thread_pool_size :
		  Returns the number of async threads in the async thread pool used for asynchro-
		  nous driver calls ( driver_async() ) as an integer.

		trace_control_word :
		  Returns  the	value  of the node's trace control word. For more information see
		  documentation of the function get_tcw in "Match Specifications in Erlang", ERTS
		  User's Guide .

		update_cpu_info :
		  The runtime system rereads the CPU information available and updates its inter-
		  nally stored information about the detected CPU topology and the amount of log-
		  ical	processors  configured	, online , and available . If the CPU information
		  has changed since the last time it was read, the atom changed is returned; oth-
		  erwise,  the atom unchanged is returned. If the CPU information has changed you
		  probably want to adjust the amount of schedulers online . You typically want to
		  have as many schedulers online as logical processors available .

		version :
		  Returns a string containing the version number of the emulator.

		wordsize :
		  Same as {wordsize, internal}

		{wordsize, internal} :
		  Returns  the size of Erlang term words in bytes as an integer, i.e. on a 32-bit
		  architecture 4 is returned, and on a pure 64-bit architecture 8 is returned. On
		  a halfword 64-bit emulator, 4 is returned, as the Erlang terms are stored using
		  a virtual wordsize of half the systems wordsize.

		{wordsize, external} :
		  Returns the true wordsize of the emulator, i.e. the size of a pointer, in bytes
		  as  an integer. On a pure 32-bit architecture 4 is returned, on both a halfword
		  and pure 64-bit architecture, 8 is returned.

   Note:
       The scheduler argument has changed name to scheduler_id . This in  order  to  avoid  mixup
       with  the  schedulers  argument. The scheduler argument was introduced in ERTS version 5.5
       and renamed in ERTS version 5.5.1.

       erlang:system_monitor() -> MonSettings

	      Types  MonSettings -> {MonitorPid, Options} | undefined
		     MonitorPid = pid()
		     Options = [Option]
		     Option = {long_gc, Time} | {large_heap, Size} | busy_port | busy_dist_port
		     Time = Size = int()

	      Returns the current system monitoring settings set  by  erlang:system_monitor/2  as
	      {MonitorPid,  Options}  ,  or  undefined if there are no settings. The order of the
	      options may be different from the one that was set.

       erlang:system_monitor(undefined | {MonitorPid, Options}) -> MonSettings

	      Types  MonitorPid, Options, MonSettings -- see below

	      When called with the argument undefined , all system  performance  monitoring  set-
	      tings are cleared.

	      Calling the function with {MonitorPid, Options} as argument, is the same as calling
	      erlang:system_monitor(MonitorPid, Options) .

	      Returns the previous system monitor settings just like erlang:system_monitor/0 .

       erlang:system_monitor(MonitorPid, [Option]) -> MonSettings

	      Types  MonitorPid = pid()
		     Option = {long_gc, Time} | {large_heap, Size} | busy_port | busy_dist_port
		     Time = Size = int()
		     MonSettings = {OldMonitorPid, [Option]}
		     OldMonitorPid = pid()

	      Sets system performance monitoring options. MonitorPid is a  local  pid  that  will
	      receive  system  monitor	messages, and the second argument is a list of monitoring
	      options:

		{long_gc, Time} :
		  If a garbage collection in the system takes at least Time  wallclock	millisec-
		  onds,  a  message {monitor, GcPid, long_gc, Info} is sent to MonitorPid . GcPid
		  is the pid that was garbage collected and Info is a list of two-element  tuples
		  describing the result of the garbage collection. One of the tuples is {timeout,
		  GcTime} where GcTime is the actual time for the garbage collection in millisec-
		  onds. The other tuples are tagged with heap_size , heap_block_size , stack_size
		  , mbuf_size , old_heap_size  ,  and  old_heap_block_size  .  These  tuples  are
		  explained   in   the	 documentation	 of   the  gc_start  trace  message  (see
		  erlang:trace/3 ). New tuples may be added, and the order of the tuples  in  the
		  Info list may be changed at any time without prior notice.

		{large_heap, Size} :
		  If  a  garbage collection in the system results in the allocated size of a heap
		  being at least Size words, a message {monitor, GcPid, large_heap, Info} is sent
		  to  MonitorPid  . GcPid and Info are the same as for long_gc above, except that
		  the tuple tagged with timeout is not present. Note : As of erts version 5.6 the
		  monitor  message is sent if the sum of the sizes of all memory blocks allocated
		  for all heap generations is equal to or larger than Size . Previously the moni-
		  tor  message was sent if the memory block allocated for the youngest generation
		  was equal to or larger than Size .

		busy_port :
		  If a process in the system gets suspended because it sends to a  busy  port,	a
		  message  {monitor,  SusPid,  busy_port, Port} is sent to MonitorPid . SusPid is
		  the pid that got suspended when sending to Port .

		busy_dist_port :
		  If a process in the system gets suspended because it sends to a  process  on	a
		  remote  node	whose inter-node communication was handled by a busy port, a mes-
		  sage {monitor, SusPid, busy_dist_port, Port} is sent to MonitorPid . SusPid  is
		  the  pid  that  got suspended when sending through the inter-node communication
		  port Port .

	      Returns the previous system monitor settings just like erlang:system_monitor/0 .

   Note:
       If a monitoring process gets so large that it itself starts to cause system  monitor  mes-
       sages  when  garbage collecting, the messages will enlarge the process's message queue and
       probably make the problem worse.

       Keep the monitoring process neat and do not set the system monitor limits too tight.

       Failure: badarg if MonitorPid does not exist.

       erlang:system_profile() -> ProfilerSettings

	      Types  ProfilerSettings -> {ProfilerPid, Options} | undefined
		     ProfilerPid = pid() | port()
		     Options = [Option]
		     Option = runnable_procs | runnable_ports | scheduler | exclusive

	      Returns the current system profiling settings  set  by  erlang:system_profile/2  as
	      {ProfilerPid,  Options}  ,  or undefined if there are no settings. The order of the
	      options may be different from the one that was set.

       erlang:system_profile(ProfilerPid, Options) -> ProfilerSettings

	      Types  ProfilerSettings -> {ProfilerPid, Options} | undefined
		     ProfilerPid = pid() | port()
		     Options = [Option]
		     Option = runnable_procs | runnable_ports | scheduler | exclusive

	      Sets system profiler options. ProfilerPid is a local pid or port that will  receive
	      profiling  messages.  The receiver is excluded from all profiling. The second argu-
	      ment is a list of profiling options:

		runnable_procs :
		  If a process is put into or removed from the run  queue  a  message,	{profile,
		  Pid, State, Mfa, Ts} , is sent to ProfilerPid . Running processes that is rein-
		  serted into the run queue after having been preemptively scheduled out will not
		  trigger this message.

		runnable_ports :
		  If  a port is put into or removed from the run queue a message, {profile, Port,
		  State, 0, Ts} , is sent to ProfilerPid .

		scheduler :
		  If a scheduler is put to sleep or awoken a message,  {profile,  scheduler,  Id,
		  State, NoScheds, Ts} , is sent to ProfilerPid .

		exclusive :
		  If  a synchronous call to a port from a process is done, the calling process is
		  considered not runnable during the  call  runtime  to  the  port.  The  calling
		  process  is notified as inactive and subsequently active when the port callback
		  returns.

   Note:
       erlang:system_profile is considered experimental and  its  behaviour  may  change  in  the
       future.

       term_to_binary(Term) -> ext_binary()

	      Types  Term = term()

	      Returns  a binary data object which is the result of encoding Term according to the
	      Erlang external term format.

	      This can be used for a variety of purposes, for example writing a term to a file in
	      an  efficient way, or sending an Erlang term to some type of communications channel
	      not supported by distributed Erlang.

	      See also binary_to_term/1 .

       term_to_binary(Term, [Option]) -> ext_binary()

	      Types  Term = term()
		     Option = compressed | {compressed,Level} | {minor_version,Version}

	      Returns a binary data object which is the result of encoding Term according to  the
	      Erlang external term format.

	      If  the option compressed is provided, the external term format will be compressed.
	      The compressed format is automatically recognized by binary_to_term/1  in  R7B  and
	      later.

	      It  is  also  possible  to  specify  a compression level by giving the option {com-
	      pressed,Level} , where Level is an integer from 0 through 9. 0 means that  no  com-
	      pression	will be done (it is the same as not giving any compressed option); 1 will
	      take the least time but may not compress as well as the higher levels; 9 will  take
	      the  most  time  and may produce a smaller result. Note the "mays" in the preceding
	      sentence; depending on the input term, level 9 compression may or may not produce a
	      smaller result than level 1 compression.

	      Currently, compressed gives the same result as {compressed,6} .

	      The option {minor_version,Version} can be use to control some details of the encod-
	      ing. This option was introduced in R11B-4. Currently, the allowed values	for  Ver-
	      sion are 0 and 1 .

	      {minor_version,1} forces any floats in the term to be encoded in a more space-effi-
	      cient and exact way (namely in the 64-bit IEEE format, rather than converted  to	a
	      textual  representation).  binary_to_term/1  in R11B-4 and later is able decode the
	      new representation.

	      {minor_version,0} is currently the default, meaning that	floats	will  be  encoded
	      using  a	textual  representation; this option is useful if you want to ensure that
	      releases prior to R11B-4 can decode resulting binary.

	      See also binary_to_term/1 .

       throw(Any)

	      Types  Any = term()

	      A non-local return from a function. If evaluated within a catch , catch will return
	      the value Any .

	      > catch throw({hello, there}).
	      {hello,there}

	      Failure: nocatch if not evaluated within a catch.

       time() -> {Hour, Minute, Second}

	      Types  Hour = Minute = Second = int()

	      Returns the current time as {Hour, Minute, Second} .

	      The time zone and daylight saving time correction depend on the underlying OS.

	      > time().
	      {9,42,44}

       tl(List1) -> List2

	      Types  List1 = List2 = [term()]

	      Returns the tail of List1 , that is, the list minus the first element.

	      > tl([geesties, guilies, beasties]).
	      [guilies, beasties]

	      Allowed in guard tests.

	      Failure: badarg if List is the empty list [].

       erlang:trace(PidSpec, How, FlagList) -> int()

	      Types  PidSpec = pid() | existing | new | all
		     How = bool()
		     FlagList = [Flag]
		     Flag -- see below

	      Turns  on  (if  How == true ) or off (if How == false ) the trace flags in FlagList
	      for the process or processes represented by PidSpec .

	      PidSpec is either a pid for a local process, or one of the following atoms:

		existing :
		  All processes currently existing.

		new :
		  All processes that will be created in the future.

		all :
		  All currently existing processes and all processes that will be created in  the
		  future.

	      FlagList	can  contain any number of the following flags (the "message tags" refers
	      to the list of messages following below):

		all :
		  Set all trace flags except {tracer, Tracer} and cpu_timestamp that are in their
		  nature different than the others.

		send :
		  Trace sending of messages.

		  Message tags: send , send_to_non_existing_process .

		'receive' :
		  Trace receiving of messages.

		  Message tags: 'receive' .

		procs :
		  Trace process related events.

		  Message  tags:  spawn  ,  exit  ,  register , unregister , link , unlink , get-
		  ting_linked , getting_unlinked .

		call :
		  Trace certain function calls. Specify which function calls to trace by  calling
		  erlang:trace_pattern/3 .

		  Message tags: call , return_from .

		silent :
		  Used	in  conjunction  with  the  call  trace  flag. The call , return_from and
		  return_to trace messages are inhibited if this flag is set, but  if  there  are
		  match specs they are executed as normal.

		  Silent  mode	is inhibited by executing erlang:trace(_, false, [silent|_]) , or
		  by a match spec executing the {silent, false} function.

		  The silent trace flag facilitates setting up a trace on many or even	all  pro-
		  cesses  in  the system. Then the interesting trace can be activated and deacti-
		  vated using the {silent,Bool} match spec function, giving a high degree of con-
		  trol of which functions with which arguments that triggers the trace.

		  Message tags: call , return_from , return_to . Or rather, the absence of.

		return_to :
		  Used	in  conjunction  with the call trace flag. Trace the actual return from a
		  traced function back to its caller. Only works for functions	traced	with  the
		  local option to erlang:trace_pattern/3 .

		  The semantics is that a trace message is sent when a call traced function actu-
		  ally returns, that is, when a chain of tail recursive  calls	is  ended.  There
		  will	be only one trace message sent per chain of tail recursive calls, why the
		  properties of tail recursiveness for function calls are kept while tracing with
		  this	flag.  Using  call and return_to trace together makes it possible to know
		  exactly in which function a process executes at any time.

		  To get  trace  messages  containing  return  values  from  functions,  use  the
		  {return_trace} match_spec action instead.

		  Message tags: return_to .

		running :
		  Trace scheduling of processes.

		  Message tags: in , and out .

		exiting :
		  Trace scheduling of an exiting processes.

		  Message tags: in_exiting , out_exiting , and out_exited .

		garbage_collection :
		  Trace garbage collections of processes.

		  Message tags: gc_start , gc_end .

		timestamp :
		  Include  a time stamp in all trace messages. The time stamp (Ts) is of the same
		  form as returned by erlang:now() .

		cpu_timestamp :
		  A global trace flag for the Erlang node that makes all trace timestamps  be  in
		  CPU  time,  not  wallclock.  It is only allowed with PidSpec==all . If the host
		  machine operating system does not support high  resolution  CPU  time  measure-
		  ments, trace/3 exits with badarg .

		arity :
		  Used	in  conjunction with the call trace flag. {M, F, Arity} will be specified
		  instead of {M, F, Args} in call trace messages.

		set_on_spawn :
		  Makes any process created by a traced process inherit its trace flags,  includ-
		  ing the set_on_spawn flag.

		set_on_first_spawn :
		  Makes  the  first  process created by a traced process inherit its trace flags,
		  excluding the set_on_first_spawn flag.

		set_on_link :
		  Makes any process linked by a traced process inherit its trace flags, including
		  the set_on_link flag.

		set_on_first_link :
		  Makes  the first process linked to by a traced process inherit its trace flags,
		  excluding the set_on_first_link flag.

		{tracer, Tracer} :
		  Specify where to send the trace messages. Tracer must be the	pid  of  a  local
		  process  or  the  port  identifier  of a local port. If this flag is not given,
		  trace messages will be sent to the process that called erlang:trace/3 .

	      The effect of combining set_on_first_link with set_on_link is the  same  as  having
	      set_on_first_link alone. Likewise for set_on_spawn and set_on_first_spawn .

	      If the timestamp flag is not given, the tracing process will receive the trace mes-
	      sages described below. Pid is the pid of the traced process  in  which  the  traced
	      event has occurred. The third element of the tuple is the message tag.

	      If  the  timestamp  flag	is given, the first element of the tuple will be trace_ts
	      instead and the timestamp is added last in the tuple.

		{trace, Pid, 'receive', Msg} :
		  When Pid receives the message Msg .

		{trace, Pid, send, Msg, To} :
		  When Pid sends the message Msg to the process To .

		{trace, Pid, send_to_non_existing_process, Msg, To} :
		  When Pid sends the message Msg to the non-existing process To .

		{trace, Pid, call, {M, F, Args}} :
		  When Pid calls a traced function. The return values of  calls  are  never  sup-
		  plied, only the call and its arguments.

		  Note	that the trace flag arity can be used to change the contents of this mes-
		  sage, so that Arity is specified instead of Args .

		{trace, Pid, return_to, {M, F, Arity}} :
		  When Pid returns to the specified function. This trace message is sent if  both
		  the  call and the return_to flags are set, and the function is set to be traced
		  on local function calls. The message is only sent when returning from  a  chain
		  of tail recursive function calls where at least one call generated a call trace
		  message (that is, the  functions  match  specification  matched  and	{message,
		  false} was not an action).

		{trace, Pid, return_from, {M, F, Arity}, ReturnValue} :
		  When Pid returns from the specified function. This trace message is sent if the
		  call	flag  is  set,	and  the  function  has  a  match  specification  with	a
		  return_trace or exception_trace action.

		{trace, Pid, exception_from, {M, F, Arity}, {Class, Value}} :
		  When Pid exits from the specified function due to an exception. This trace mes-
		  sage is sent if the call flag is set, and the function has a	match  specifica-
		  tion with an exception_trace action.

		{trace, Pid, spawn, Pid2, {M, F, Args}} :
		  When	Pid  spawns  a new process Pid2 with the specified function call as entry
		  point.

		  Note that Args is supposed to be the argument list, but may be any term in  the
		  case of an erroneous spawn.

		{trace, Pid, exit, Reason} :
		  When Pid exits with reason Reason .

		{trace, Pid, link, Pid2} :
		  When Pid links to a process Pid2 .

		{trace, Pid, unlink, Pid2} :
		  When Pid removes the link from a process Pid2 .

		{trace, Pid, getting_linked, Pid2} :
		  When Pid gets linked to a process Pid2 .

		{trace, Pid, getting_unlinked, Pid2} :
		  When Pid gets unlinked from a process Pid2 .

		{trace, Pid, register, RegName} :
		  When Pid gets the name RegName registered.

		{trace, Pid, unregister, RegName} :
		  When	Pid  gets the name RegName unregistered. Note that this is done automati-
		  cally when a registered process exits.

		{trace, Pid, in, {M, F, Arity} | 0} :
		  When Pid is scheduled to run. The process will run in function {M, F, Arity}	.
		  On some rare occasions the current function cannot be determined, then the last
		  element Arity is 0.

		{trace, Pid, out, {M, F, Arity} | 0} :
		  When Pid is scheduled out. The process was running in function {M,  F,  Arity}.
		  On some rare occasions the current function cannot be determined, then the last
		  element Arity is 0.

		{trace, Pid, gc_start, Info} :
		  Sent when garbage collection is about to be started. Info is a list of two-ele-
		  ment tuples, where the first element is a key, and the second is the value. You
		  should not depend on the tuples have any defined order. Currently, the  follow-
		  ing keys are defined:

		  heap_size :
		    The size of the used part of the heap.

		  heap_block_size :
		    The size of the memory block used for storing the heap and the stack.

		  old_heap_size :
		    The size of the used part of the old heap.

		  old_heap_block_size :
		    The size of the memory block used for storing the old heap.

		  stack_size :
		    The actual size of the stack.

		  recent_size :
		    The size of the data that survived the previous garbage collection.

		  mbuf_size :
		    The combined size of message buffers associated with the process.

		  bin_vheap_size :
		    The total size of unique off-heap binaries referenced from the process heap.

		  bin_vheap_block_size :
		    The  total	size  of  binaries,  in words, allowed in the virtual heap in the
		    process before doing a garbage collection.

		  bin_old_vheap_size :
		    The total size of unique off-heap binaries referenced from	the  process  old
		    heap.

		  bin_vheap_block_size :
		    The  total size of binaries, in words, allowed in the virtual old heap in the
		    process before doing a garbage collection.

		  All sizes are in words.

		{trace, Pid, gc_end, Info} :
		  Sent when garbage collection is finished. Info contains the same kind  of  list
		  as  in  the gc_start message, but the sizes reflect the new sizes after garbage
		  collection.

	      If the tracing process dies, the flags will be silently removed.

	      Only one process can trace a particular process. For this reason, attempts to trace
	      an already traced process will fail.

	      Returns: A number indicating the number of processes that matched PidSpec . If Pid-
	      Spec is a pid, the return value will be 1 . If  PidSpec  is  all	or  existing  the
	      return  value  will be the number of processes running, excluding tracer processes.
	      If PidSpec is new , the return value will be 0 .

	      Failure: If specified arguments are not supported. For example cpu_timestamp is not
	      supported on all platforms.

       erlang:trace_delivered(Tracee) -> Ref

	      Types  Tracee = pid() | all
		     Ref = reference()

	      The  delivery  of  trace	messages is dislocated on the time-line compared to other
	      events in the system. If you know that the Tracee has passed some specific point in
	      its  execution, and you want to know when at least all trace messages corresponding
	      to events up to this point have reached the tracer you can use  erlang:trace_deliv-
	      ered(Tracee)  .  A  {trace_delivered, Tracee, Ref} message is sent to the caller of
	      erlang:trace_delivered(Tracee) when it is guaranteed that all trace  messages  have
	      been  delivered  to  the	tracer up to the point that the Tracee had reached at the
	      time of the call to erlang:trace_delivered(Tracee) .

	      Note that the trace_delivered message does not imply that trace messages have  been
	      delivered;  instead,  it	implies  that all trace messages that should be delivered
	      have been delivered. It is not an error if Tracee isn't, and hasn't been traced  by
	      someone,	but  if this is the case, no trace messages will have been delivered when
	      the trace_delivered message arrives.

	      Note that Tracee has to refer to a process currently, or previously existing on the
	      same  node  as the caller of erlang:trace_delivered(Tracee) resides on. The special
	      Tracee atom all denotes all processes that currently are traced in the node.

	      An example: Process A is tracee, port B is tracer, and process C is the port  owner
	      of B . C wants to close B when A exits. C can ensure that the trace isn't truncated
	      by calling erlang:trace_delivered(A) when A exits and wait  for  the  {trace_deliv-
	      ered, A, Ref} message before closing B .

	      Failure:	badarg	if Tracee does not refer to a process (dead or alive) on the same
	      node as the caller of erlang:trace_delivered(Tracee) resides on.

       erlang:trace_info(PidOrFunc, Item) -> Res

	      Types  PidOrFunc = pid() | new | {Module, Function, Arity} | on_load
		     Module = Function = atom()
		     Arity = int()
		     Item, Res -- see below

	      Returns trace information about a process or function.

	      To get information about a process, PidOrFunc should be a pid or the atom new . The
	      atom  new  means	that  the default trace state for processes to be created will be
	      returned. Item must have one of the following values:

		flags :
		  Return a list of atoms indicating what  kind	of  traces  is	enabled  for  the
		  process.  The  list  will be empty if no traces are enabled, and one or more of
		  the followings atoms if traces are enabled: send , 'receive' ,  set_on_spawn	,
		  call	,  return_to  ,  procs	,  set_on_first_spawn  ,  set_on_link , running ,
		  garbage_collection , timestamp , and arity . The order is arbitrary.

		tracer :
		  Return the identifier for process or port tracing this process. If this process
		  is not being traced, the return value will be [] .

	      To  get  information  about  a function, PidOrFunc should be a three-element tuple:
	      {Module, Function, Arity} or the atom on_load . No wildcards are	allowed.  Returns
	      undefined  if the function does not exist or false if the function is not traced at
	      all. Item must have one of the following values:

		traced :
		  Return global if this function is traced on global  function	calls,	local  if
		  this	function is traced on local function calls (i.e local and global function
		  calls), and false if neither local nor global function calls are traced.

		match_spec :
		  Return the match specification for this function, if it has one. If  the  func-
		  tion	is locally or globally traced but has no match specification defined, the
		  returned value is [] .

		meta :
		  Return the meta trace tracer process or port for this function, if it has  one.
		  If  the  function  is  not meta traced the returned value is false , and if the
		  function is meta traced but has once detected that the tracer proc is  invalid,
		  the returned value is [].

		meta_match_spec :
		  Return  the meta trace match specification for this function, if it has one. If
		  the function is meta	traced	but  has  no  match  specification  defined,  the
		  returned value is [] .

		call_count :
		  Return  the  call count value for this function or true for the pseudo function
		  on_load if call count tracing is  active.  Return  false  otherwise.	See  also
		  erlang:trace_pattern/3 .

		call_time :
		  Return  the  call time values for this function or true for the pseudo function
		  on_load if call time tracing is active. Returns false otherwise. The call  time
		  values  returned,  [{Pid,  Count,  S, Us}] , is a list of each process that has
		  executed the function and its specific  counters.  See  also	erlang:trace_pat-
		  tern/3 .

		all :
		  Return  a  list  containing  the  {Item,  Value} tuples for all other items, or
		  return false if no tracing is active for this function.

	      The actual return value will be {Item, Value} , where Value is the requested infor-
	      mation  as described above. If a pid for a dead process was given, or the name of a
	      non-existing function, Value will be undefined .

	      If PidOrFunc is the on_load , the information returned refers to the default  value
	      for code that will be loaded.

       erlang:trace_pattern(MFA, MatchSpec) -> int()

	      The  same  as erlang:trace_pattern(MFA, MatchSpec, []) , retained for backward com-
	      patibility.

       erlang:trace_pattern(MFA, MatchSpec, FlagList) -> int()

	      Types  MFA, MatchSpec, FlagList -- see below

	      This BIF is used to enable or disable call tracing for exported functions. It  must
	      be  combined  with  erlang:trace/3  to set the call trace flag for one or more pro-
	      cesses.

	      Conceptually, call tracing works like this: Inside the Erlang virtual machine there
	      is  a  set  of  processes to be traced and a set of functions to be traced. Tracing
	      will be enabled on the intersection of the set. That is, if a process  included  in
	      the  traced  process  set calls a function included in the traced function set, the
	      trace action will be taken. Otherwise, nothing will happen.

	      Use erlang:trace/3 to add or remove one or more processes to the set of traced pro-
	      cesses.  Use  erlang:trace_pattern/2 to add or remove exported functions to the set
	      of traced functions.

	      The erlang:trace_pattern/3 BIF can also add match  specifications  to  an  exported
	      function. A match specification comprises a pattern that the arguments to the func-
	      tion must match, a guard expression which must evaluate to true and an action to be
	      performed.  The  default action is to send a trace message. If the pattern does not
	      match or the guard fails, the action will not be executed.

	      The MFA argument should be a tuple like  {Module,  Function,  Arity}  or	the  atom
	      on_load  (described  below).  It	can  be  the  module,  function, and arity for an
	      exported function (or a BIF in any module). The '_' atom can be used to mean any of
	      that kind. Wildcards can be used in any of the following ways:

		{Module,Function,'_'} :
		  All exported functions of any arity named Function in module Module .

		{Module,'_','_'} :
		  All exported functions in module Module .

		{'_','_','_'} :
		  All exported functions in all loaded modules.

	      Other  combinations,  such as {Module,'_',Arity} , are not allowed. Local functions
	      will match wildcards only if the local option is in the FlagList .

	      If the MFA argument is the atom on_load , the match  specification  and  flag  list
	      will be used on all modules that are newly loaded.

	      The MatchSpec argument can take any of the following forms:

		false :
		  Disable  tracing  for the matching function(s). Any match specification will be
		  removed.

		true :
		  Enable tracing for the matching function(s).

		MatchSpecList :
		  A list of match specifications. An empty list is equivalent to true .  See  the
		  ERTS User's Guide for a description of match specifications.

		restart :
		  For  the  FlagList option call_count and call_time : restart the existing coun-
		  ters. The behaviour is undefined for other FlagList options.

		pause :
		  For the FlagList option call_count and call_time : pause the existing counters.
		  The behaviour is undefined for other FlagList options.

	      The FlagList parameter is a list of options. The following options are allowed:

		global :
		  Turn	on or off call tracing for global function calls (that is, calls specify-
		  ing the module explicitly). Only exported functions will match and only  global
		  calls will generate trace messages. This is the default.

		local :
		  Turn	on  or	off  call tracing for all types of function calls. Trace messages
		  will be sent whenever any of the specified functions are called, regardless  of
		  how  they are called. If the return_to flag is set for the process, a return_to
		  message will also be sent when this function returns to its caller.

		meta | {meta, Pid} :
		  Turn on or off meta tracing for all types of	function  calls.  Trace  messages
		  will	be  sent  to the tracer process or port Pid whenever any of the specified
		  functions are called, regardless of how they are called. If no  Pid  is  speci-
		  fied, self() is used as a default tracer process.

		  Meta	tracing  traces  all  processes and does not care about the process trace
		  flags set by trace/3 , the trace flags are instead fixed to [call, timestamp] .

		  The match spec function {return_trace} works with meta trace and send its trace
		  message to the same tracer process.

		call_count :
		  Starts ( MatchSpec == true ) or stops ( MatchSpec == false ) call count tracing
		  for all types of function calls. For every function a  counter  is  incremented
		  when	the function is called, in any process. No process trace flags need to be
		  activated.

		  If call count tracing is started while already running, the count is	restarted
		  from	zero. Running counters can be paused with MatchSpec == pause . Paused and
		  running counters can be restarted from zero with MatchSpec == restart .

		  The counter value can be read with erlang:trace_info/2 .

		call_time :
		  Starts ( MatchSpec == true ) or stops ( MatchSpec == false ) call time  tracing
		  for  all  types  of function calls. For every function a counter is incremented
		  when the function is called. Time spent in the function is accumulated  in  two
		  other  counters,  seconds  and  micro-seconds. The counters are stored for each
		  call traced process.

		  If call time tracing is started while already running, the count  and  time  is
		  restarted  from  zero. Running counters can be paused with MatchSpec == pause .
		  Paused and running counters can  be  restarted  from	zero  with  MatchSpec  ==
		  restart .

		  The counter value can be read with erlang:trace_info/2 .

	      The  global  and local options are mutually exclusive and global is the default (if
	      no options are specified). The call_count and meta options perform a kind of  local
	      tracing,	and can also not be combined with global . A function can be either glob-
	      ally or locally traced. If global tracing is specified for a specified set of func-
	      tions;  local, meta, call time and call count tracing for the matching set of local
	      functions will be disabled, and vice versa.

	      When disabling trace, the option must match the type of trace that is  set  on  the
	      function,  so  that local tracing must be disabled with the local option and global
	      tracing with the global option (or no option at all), and so forth.

	      There is no way to directly change part of a match specification list. If  a  func-
	      tion  has  a  match specification, you can replace it with a completely new one. If
	      you need to change an existing match specification, use the erlang:trace_info/2 BIF
	      to retrieve the existing match specification.

	      Returns  the  number of exported functions that matched the MFA argument. This will
	      be zero if none matched at all.

       trunc(Number) -> int()

	      Types  Number = number()

	      Returns an integer by the truncating Number .

	      > trunc(5.5).
	      5

	      Allowed in guard tests.

       tuple_size(Tuple) -> int()

	      Types  Tuple = tuple()

	      Returns an integer which is the number of elements in Tuple .

	      > tuple_size({morni, mulle, bwange}).
	      3

	      Allowed in guard tests.

       tuple_to_list(Tuple) -> [term()]

	      Types  Tuple = tuple()

	      Returns a list which corresponds to Tuple . Tuple may contain any Erlang terms.

	      > tuple_to_list({share, {'Ericsson_B', 163}}).
	      [share,{'Ericsson_B',163}]

       erlang:universaltime() -> {Date, Time}

	      Types  Date = {Year, Month, Day}
		     Time = {Hour, Minute, Second}
		     Year = Month = Day = Hour = Minute = Second = int()

	      Returns the current date and time according to Universal	Time  Coordinated  (UTC),
	      also  called  GMT, in the form {{Year, Month, Day}, {Hour, Minute, Second}} if sup-
	      ported by the underlying operating system. If not, erlang:universaltime() is equiv-
	      alent to erlang:localtime() .

	      > erlang:universaltime().
	      {{1996,11,6},{14,18,43}}

       erlang:universaltime_to_localtime({Date1, Time1}) -> {Date2, Time2}

	      Types  Date1 = Date2 = {Year, Month, Day}
		     Time1 = Time2 = {Hour, Minute, Second}
		     Year = Month = Day = Hour = Minute = Second = int()

	      Converts	Universal Time Coordinated (UTC) date and time to local date and time, if
	      this is supported by the underlying OS.  Otherwise,  no  conversion  is  done,  and
	      {Date1, Time1} is returned.

	      > erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).
	      {{1996,11,7},{15,18,43}}

	      Failure: badarg if Date1 or Time1 do not denote a valid date or time.

       unlink(Id) -> true

	      Types  Id = pid() | port()

	      Removes  the  link, if there is one, between the calling process and the process or
	      port referred to by Id .

	      Returns true and does not fail, even if there is no link to Id , or if Id does  not
	      exist.

	      Once  unlink(Id) has returned it is guaranteed that the link between the caller and
	      the entity referred to by Id has no effect on the caller in the future (unless  the
	      link  is	setup again). If caller is trapping exits, an {'EXIT', Id, _} message due
	      to the link might have been placed in the callers message queue prior to the  call,
	      though.  Note,  the  {'EXIT', Id, _} message can be the result of the link, but can
	      also be the result of Id calling exit/2 .  Therefore,  it  may  be  appropriate  to
	      cleanup  the  message  queue  when trapping exits after the call to unlink(Id) , as
	      follow:

		  unlink(Id),
		  receive
		      {'EXIT', Id, _} ->
			  true
		  after 0 ->
			  true
		  end

   Note:
       Prior to OTP release R11B (erts version 5.5)  unlink/1  behaved	completely  asynchronous,
       i.e.,  the  link  was active until the "unlink signal" reached the linked entity. This had
       one undesirable effect, though. You could never know when you were guaranteed  not  to  be
       effected by the link.

       Current	behavior can be viewed as two combined operations: asynchronously send an "unlink
       signal" to the linked entity and ignore any future results of the link.

       unregister(RegName) -> true

	      Types  RegName = atom()

	      Removes the registered name RegName , associated with a pid or a port identifier.

	      > unregister(db).
	      true

	      Users are advised not to unregister system processes.

	      Failure: badarg if RegName is not a registered name.

       whereis(RegName) -> pid() | port() | undefined

	      Returns the pid or port identifier with the registered name RegName . Returns unde-
	      fined if the name is not registered.

	      > whereis(db).
	      <0.43.0>

       erlang:yield() -> true

	      Voluntarily   let  other	processes  (if	any)  get  a  chance  to  execute.  Using
	      erlang:yield() is similar to receive after 1 -> ok end ,	except	that  yield()  is
	      faster.

   Warning:
       There is seldom or never any need to use this BIF, especially in the SMP-emulator as other
       processes will have a chance to run in another scheduler thread	anyway.  Using	this  BIF
       without a thorough grasp of how the scheduler works may cause performance degradation.

Ericsson AB				    erts 5.8.3				     erlang(3erl)
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