EQN(7)						       BSD Miscellaneous Information Manual						    EQN(7)

NAME

     eqn -- eqn language reference for mandoc

DESCRIPTION

     The eqn language is an equation-formatting language.  It is used within mdoc(7) and man(7) UNIX manual pages.  It describes the structure of
     an equation, not its mathematical meaning.  This manual describes the eqn language accepted by the mandoc(1) utility, which corresponds to
     the Second Edition eqn specification (see SEE ALSO for references).

     Equations within mdoc(7) or man(7) documents are enclosed by the standalone '.EQ' and '.EN' tags.	Equations are multi-line blocks consisting
     of formulas and control statements.

EQUATION STRUCTURE

     Each equation is bracketed by '.EQ' and '.EN' strings.  Note: these are not the same as roff(7) macros, and may only be invoked as '.EQ'.

     The equation grammar is as follows, where quoted strings are case-sensitive literals in the input:

	   eqn	   : box | eqn box
	   box	   : text
		   | "{" eqn "}"
		   | "define" text text
		   | "ndefine" text text
		   | "tdefine" text text
		   | "gfont" text
		   | "gsize" text
		   | "set" text text
		   | "undef" text
		   | "sqrt" box
		   | box pos box
		   | box mark
		   | "matrix" "{" [col "{" list "}" ]*
		   | pile "{" list "}"
		   | font box
		   | "size" text box
		   | "left" text eqn ["right" text]
	   col	   : "lcol" | "rcol" | "ccol" | "col"
	   text    : [^space"]+ | ".*"
	   pile    : "lpile" | "cpile" | "rpile" | "pile"
	   pos	   : "over" | "sup" | "sub" | "to" | "from"
	   mark    : "dot" | "dotdot" | "hat" | "tilde" | "vec"
		   | "dyad" | "bar" | "under"
	   font    : "roman" | "italic" | "bold" | "fat"
	   list    : eqn
		   | list "above" eqn
	   space   : [^~ 	]

     White-space consists of the space, tab, circumflex, and tilde characters.	It is required to delimit tokens consisting of alphabetic charac-
     ters and it is ignored at other places.  Braces and quotes also delimit tokens.  If within a quoted string, these space characters are
     retained.	Quoted strings are also not scanned for keywords, glyph names, and expansion of definitions.  To print a literal quote character,
     it can be prepended with a backslash or expressed with the (dq escape sequence.

     Subequations can be enclosed in braces to pass them as arguments to operation keywords, overriding standard operation precedence.	Braces can
     be nested.  To set a brace verbatim, it needs to be enclosed in quotes.

     The following text terms are translated into a rendered glyph, if available: alpha, beta, chi, delta, epsilon, eta, gamma, iota, kappa,
     lambda, mu, nu, omega, omicron, phi, pi, psi, rho, sigma, tau, theta, upsilon, xi, zeta, DELTA, GAMMA, LAMBDA, OMEGA, PHI, PI, PSI, SIGMA,
     THETA, UPSILON, XI, inter (intersection), union (union), prod (product), int (integral), sum (summation), grad (gradient), del (vector dif-
     ferential), times (multiply), cdot (centre-dot), nothing (zero-width space), approx (approximately equals), prime (prime), half (one-half),
     partial (partial differential), inf (infinity), >> (much greater), << (much less), -> (left arrow), <- (right arrow), +- (plus-minus), !=
     (not equal), == (equivalence), <= (less-than-equal), and >= (more-than-equal).  The character escape sequences documented in mandoc_char(7)
     can be used, too.

     The following control statements are available:

     define  Replace all occurrences of a key with a value.  Its syntax is as follows:

		   define key cvalc

	     The first character of the value string, c, is used as the delimiter for the value val.  This allows for arbitrary enclosure of terms
	     (not just quotes), such as

		   define foo 'bar baz'
		   define foo cbar bazc

	     It is an error to have an empty key or val.  Note that a quoted key causes errors in some eqn implementations and should not be con-
	     sidered portable.	It is not expanded for replacements.  Definitions may refer to other definitions; these are evaluated recursively
	     when text replacement occurs and not when the definition is created.

	     Definitions can create arbitrary strings, for example, the following is a legal construction.

		   define foo 'define'
		   foo bar 'baz'

	     Self-referencing definitions will raise an error.	The ndefine statement is a synonym for define, while tdefine is discarded.

     gfont   Set the default font of subsequent output.  Its syntax is as follows:

		   gfont font

	     In mandoc, this value is discarded.

     gsize   Set the default size of subsequent output.  Its syntax is as follows:

		   gsize [+|-]size

	     The size value should be an integer.  If prepended by a sign, the font size is changed relative to the current size.

     set     Set an equation mode.  In mandoc, both arguments are thrown away.	Its syntax is as follows:

		   set key val

	     The key and val are not expanded for replacements.  This statement is a GNU extension.

     undef   Unset a previously-defined key.  Its syntax is as follows:

		   define key

	     Once invoked, the definition for key is discarded.  The key is not expanded for replacements.  This statement is a GNU extension.

     Operation keywords have the following semantics:

     above   See pile.

     bar     Draw a line over the preceding box.

     bold    Set the following box using bold font.

     ccol    Like cpile, but for use in matrix.

     cpile   Like pile, but with slightly increased vertical spacing.

     dot     Set a single dot over the preceding box.

     dotdot  Set two dots (dieresis) over the preceding box.

     dyad    Set a dyad symbol (left-right arrow) over the preceding box.

     fat     A synonym for bold.

     font    Set the second argument using the font specified by the first argument; currently not recognized by the mandoc(1) eqn parser.

     from    Set the following box below the preceding box, using a slightly smaller font.  Used for sums, integrals, limits, and the like.

     hat     Set a hat (circumflex) over the preceding box.

     italic  Set the following box using italic font.

     lcol    Like lpile, but for use in matrix.

     left    Set the first argument as a big left delimiter before the second argument.  As an optional third argument, right can follow.  In that
	     case, the fourth argument is set as a big right delimiter after the second argument.

     lpile   Like cpile, but subequations are left-justified.

     matrix  Followed by a list of columns enclosed in braces.	All columns need to have the same number of subequations.  The columns are set as
	     a matrix.	The difference compared to multiple subsequent pile operators is that in a matrix, corresponding subequations in all col-
	     umns line up horizontally, while each pile does vertical spacing independently.

     over    Set a fraction.  The preceding box is the numerator, the following box is the denominator.

     pile    Followed by a list of subequations enclosed in braces, the subequations being separated by above keywords.  Sets the subequations one
	     above the other, each of them centered.  Typically used to represent vectors in coordinate representation.

     rcol    Like rpile, but for use in matrix.

     right   See left; right cannot be used without left.  To set a big right delimiter without a big left delimiter, the following construction
	     can be used:

		   left "" box right delimiter

     roman   Set the following box using the default font.

     rpile   Like cpile, but subequations are right-justified.

     size    Set the second argument with the font size specified by the first argument; currently ignored by mandoc(1).  By prepending a plus or
	     minus sign to the first argument, the font size can be selected relative to the current size.

     sqrt    Set the square root of the following box.

     sub     Set the following box as a subscript to the preceding box.

     sup     Set the following box as a superscript to the preceding box.  As a special case, if a sup clause immediately follows a sub clause as
	     in

		   mainbox sub subbox sup supbox

	     both are set with respect to the same mainbox, that is, supbox is set above subbox.

     tilde   Set a tilde over the preceding box.

     to      Set the following box above the preceding box, using a slightly smaller font.  Used for sums and integrals and the like.  As a spe-
	     cial case, if a to clause immediately follows a from clause as in

		   mainbox from frombox to tobox

	     both are set below and above the same mainbox.

     under   Underline the preceding box.

     vec     Set a vector symbol (right arrow) over the preceding box.

     The binary operations from, to, sub, and sup group to the right, that is,

	   mainbox sup supbox sub subbox

     is the same as

	   mainbox sup {supbox sub subbox}

     and different from

	   {mainbox sup supbox} sub subbox.

     By contrast, over groups to the left.

     In the following list, earlier operations bind more tightly than later operations:

     1.   dyad, vec, under, bar, tilde, hat, dot, dotdot
     2.   fat, roman, italic, bold, size
     3.   sub, sup
     4.   sqrt
     5.   over
     6.   from, to

COMPATIBILITY

     This section documents the compatibility of mandoc eqn and the troff eqn implementation (including GNU troff).

     -	 The text string '"' is interpreted as a literal quote in troff.  In mandoc, this is interpreted as a comment.
     -	 In troff, The circumflex and tilde white-space symbols map to fixed-width spaces.  In mandoc, these characters are synonyms for the space
	 character.
     -	 The troff implementation of eqn allows for equation alignment with the mark and lineup tokens.  mandoc discards these tokens.	The back
	 n, fwd n, up n, and down n commands are also ignored.
     -	 Inline equations and the delim control statement are not yet implemented in mandoc(1).

SEE ALSO

     mandoc(1), man(7), mandoc_char(7), mdoc(7), roff(7)

     Brian W. Kernighan and Lorinda L. Cherry, "System for Typesetting Mathematics", Communications of the ACM, 18, 151-157, March, 1975.

     Brian W. Kernighan and Lorinda L. Cherry, Typesetting Mathematics, User's Guide, 1976.

     Brian W. Kernighan and Lorinda L. Cherry, Typesetting Mathematics, User's Guide (Second Edition), 1978.

HISTORY

     The eqn utility, a preprocessor for troff, was originally written by Brian W. Kernighan and Lorinda L. Cherry in 1975.  The GNU reimplementa-
     tion of eqn, part of the GNU troff package, was released in 1989 by James Clark.  The eqn component of mandoc(1) was added in 2011.

AUTHORS

     This eqn reference was written by Kristaps Dzonsons <kristaps@bsd.lv>.

BSD
								 October 12, 2014							       BSD