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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 Sec-
     ond Edition eqn specification (see	SEE ALSO for references).

     Equations within mdoc(7) or man(7)	documents are enclosed by the stand-
     alone `.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-sensi-
     tive 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   : [\^~ \t]

     White-space consists of the space,	tab, circumflex, and tilde characters.
     It	is required to delimit tokens consisting of alphabetic characters 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 oper-
     ation 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 avail-
     able: 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 differential),
     times (multiply), cdot (center-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 char-
     acter 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	delim-
	     iter 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
	     considered	portable.  It is not expanded for replacements.	 Defi-
	     nitions may refer to other	definitions; these are evaluated
	     recursively when text replacement occurs and not when the defini-
	     tion is created.

	     Definitions can create arbitrary strings, for example, the	fol-
	     lowing 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 fol-
	     lows:

		   gfont font

	     In	mandoc,	this value is discarded.

     gsize   Set the default size of subsequent	output.	 Its syntax is as fol-
	     lows:

		   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 state-
	     ment 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 exten-
	     sion.

     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 columns line up horizontally, while each pile does vertical
	     spacing independently.

     over    Set a fraction.  The preceding box	is the numerator, the follow-
	     ing box is	the denominator.

     pile    Followed by a list	of subequations	enclosed in braces, the	sube-
	     quations being separated by above keywords.  Sets the subequa-
	     tions 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 construc-
	     tion 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
	     special 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.

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 4, 2017			   BSD

NAME | DESCRIPTION | EQUATION STRUCTURE | COMPATIBILITY | SEE ALSO | HISTORY | AUTHORS

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