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   : [\^~ \t]

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 differential), 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 considered 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, Lorinda L. Cherry, System for Typesetting Mathematics, Communications of the ACM, 18, 151–157, March, 1975. Brian W. Kernighan, Lorinda L. Cherry, Typesetting Mathematics, User's Guide, 1976. Brian W. Kernighan, 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 reimplementation 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>.