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
		   | 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.	If within a quoted string, these space characters are retained.
     Quoted strings are also not scanned for replacement definitions.

     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 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.

     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.

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.

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
								September 25, 2011							       BSD