eqn(1)                      General Commands Manual                     eqn(1)

Name
       eqn - format mathematics (equations) for groff or MathML

Synopsis
       eqn [-CNrR] [-d xy] [-f F] [-m n] [-M dir] [-p n] [-s n] [-T dev]
           [file_...]

       eqn --help

       eqn -v
       eqn --version

Description
       The GNU implementation of eqn is part of the groff(7) document
       formatting system.  eqn is a troff(1) preprocessor that translates
       expressions in its own language, embedded in roff(7) input files, into
       mathematical notation typeset by troff(1).  It copies each file's
       contents to the standard output stream, translating each equation
       between lines starting with .EQ and .EN, or within a pair of user-
       specified delimiters.  Normally, eqn is not executed directly by the
       user, but invoked by specifying the -e option to groff(1).  While GNU
       eqn's input syntax is highly compatible with AT&T eqn, the output eqn
       produces cannot be processed by AT&T troff; GNU troff (or a troff
       implementing relevant GNU extensions) must be used.  If no file
       operands are given on the command line, or if file is “-”, eqn reads
       the standard input stream.

       Unless the -R option is used, eqn searches for the file eqnrc in the
       directories given with the -M option first, then in
       /opt/homebrew/etc/groff/site-tmac, and finally in the standard macro
       directory /opt/homebrew/Cellar/groff/1.23.0_1/share/groff/1.23.0/tmac.
       If it exists and is readable, eqn processes it before any input files.

       This man page primarily discusses the differences between GNU eqn and
       AT&T eqn.  Most of the new features of the GNU eqn input language are
       based on TeX.  There are some references to the differences between TeX
       and GNU eqn below; these may safely be ignored if you do not know TeX.

       Three points are worth special note.

       • GNU eqn emits Presentation MathML output when invoked with the
         “-T MathML” option.

       • GNU eqn does not support terminal devices well, though it may suffice
         for simple inputs.

       • GNU eqn sets the input token “...” as an ellipsis on the text
         baseline, not the three centered dots of AT&T eqn.  Set an ellipsis
         on the math axis with the GNU extension macro cdots.

   Anatomy of an equation
       eqn input consists of tokens.  Consider a form of Newton's second law
       of motion.  The input

              .EQ
              F =
              m a
              .EN

       becomes F = m a. Each of F, =, m, and a is a token.  Spaces and
       newlines are interchangeable; they separate tokens but do not break
       lines or produce space in the output.

       The following input characters not only separate tokens, but manage
       their grouping and spacing as well.

       { }    Braces perform grouping.  Whereas “e sup a b” expresses “(e to
              the a) times b”, “e sup { a b }” means “e to the (a times b)”.
              When immediately preceded by a “left” or “right” primitive, a
              brace loses its special meaning.

       ^ ~    are the half space and full space, respectively.  Use them to
              tune the appearance of the output.

       Tab and leader characters separate tokens as well as advancing the
       drawing position to the next tab stop, but are seldom used in eqn
       input.  When they occur, they must appear at the outermost lexical
       scope.  This roughly means that they can't appear within braces that
       are necessary to disambiguate the input; eqn will diagnose an error in
       this event.  (See subsection “Macros” below for additional token
       separation rules.)

       Other tokens are primitives, macros, an argument to either of the
       foregoing, or components of an equation.

       Primitives are fundamental keywords of the eqn language.  They can
       configure an aspect of the preprocessor's state, as when setting a
       “global” font selection or type size (gfont and gsize), or declaring or
       deleting macros (“define” and undef); these are termed commands.  Other
       primitives perform formatting operations on the tokens after them (as
       with fat, over, sqrt, or up).

       Equation components include mathematical variables, constants, numeric
       literals, and operators.  eqn remaps some input character sequences to
       groff special character escape sequences for economy in equation entry
       and to ensure that glyphs from an unstyled font are used; see
       groff_char(7).


              +   \[pl]                '    \[fm]
              -   \[mi]                <=   \[<=]
              =   \[eq]                >=   \[>=]

       Macros permit primitives, components, and other macros to be collected
       and referred to by a single token.  Predefined macros make convenient
       the preparation of eqn input in a form resembling its spoken
       expression; for example, consider cos, hat, inf, and lim.

   Spacing and typeface
       GNU eqn imputes types to the components of an equation, adjusting the
       spacing between them accordingly.  Recognized types are as follows;
       most affect spacing only, whereas the “letter” subtype of “ordinary”
       also assigns a style.

         ordinary      character such as “1”, “a”, or “!”
          letter       character to be italicized by default
          digit        n/a
         operator      large operator such as “Σ”
         binary        binary operator such as “+”
         relation      relational operator such as “=”
         opening       opening bracket such as “(”
         closing       closing bracket such as “)”
         punctuation   punctuation character such as “,”
         inner         sub-formula contained within brackets
         suppress      component to which automatic spacing is not applied

       Two primitives apply types to equation components.

       type t e
              Apply type t to expression e.

       chartype t text
              Assign each character in (unquoted) text type t, persistently.

       eqn sets up spacings and styles as if by the following commands.


              chartype "letter"      abcdefghiklmnopqrstuvwxyz
              chartype "letter"      ABCDEFGHIKLMNOPQRSTUVWXYZ
              chartype "letter"      \[*a]\[*b]\[*g]\[*d]\[*e]\[*z]
              chartype "letter"      \[*y]\[*h]\[*i]\[*k]\[*l]\[*m]
              chartype "letter"      \[*n]\[*c]\[*o]\[*p]\[*r]\[*s]
              chartype "letter"      \[*t]\[*u]\[*f]\[*x]\[*q]\[*w]
              chartype "binary"      *\[pl]\[mi]
              chartype "relation"    <>\[eq]\[<=]\[>=]
              chartype "opening"     {([
              chartype "closing"     })]
              chartype "punctuation" ,;:.
              chartype "suppress"    ^~

       eqn assigns all other ordinary and special roff characters, including
       numerals 0–9, the “ordinary” type.  (The “digit” type is not used, but
       is available for customization.)  In keeping with common practice in
       mathematical typesetting, lowercase, but not uppercase, Greek letters
       are assigned the “letter” type to style them in italics.  The macros
       for producing ellipses, “...”, cdots, and ldots, use the “inner” type.

   Primitives
       eqn supports without alteration the AT&T eqn primitives above, back,
       bar, bold, define, down, fat, font, from, fwd, gfont, gsize, italic,
       left, lineup, mark, matrix, ndefine, over, right, roman, size, sqrt,
       sub, sup, tdefine, to, under, and up.

   New primitives
       The GNU extension primitives “type” and chartype are discussed in
       subsection “Spacing and typeface” above; “set” in subsection
       “Customization” below; and grfont and gbfont in subsection “Fonts”
       below.  In the following synopses, X can be any character not appearing
       in the parameter thus bracketed.

       e1 accent e2
              Set e2 as an accent over e1.  e2 is assumed to be at the
              appropriate height for a lowercase letter without an ascender;
              eqn vertically shifts it depending on e1's height.  For example,
              hat is defined as follows.

                     accent { "^" }

              dotdot, dot, tilde, vec, and dyad are also defined using the
              accent primitive.

       big e  Enlarge the expression e; semantics like those of CSS “large”
              are intended.  In troff output, the type size is increased by 5
              scaled points.  MathML output emits the following.

                     <mstyle mathsize='big'>

       copy file
       include file
              Interpolate the contents of file, omitting lines beginning with
              .EQ or .EN.  If a relative path name, file is sought relative to
              the current working directory.

       ifdef name X anything X
              If name is defined as a primitive or macro, interpret anything.

       nosplit text
              As "text", but since text is not quoted it is subject to macro
              expansion; it is not split up and the spacing between characters
              not adjusted per subsection “Spacing and typeface” above.

       e_opprime
              As prime, but set the prime symbol as an operator on e.  In the
              input “A opprime sub 1”, the “1” is tucked under the prime as a
              subscript to the “A” (as is conventional in mathematical
              typesetting), whereas when prime is used, the “1” is a subscript
              to the prime character.  The precedence of opprime is the same
              as that of bar and “under”, and higher than that of other
              primitives except accent and uaccent.  In unquoted text, a
              neutral apostrophe (') that is not the first character on the
              input line is treated like opprime.

       sdefine name X anything X
              As “define”, but name is not recognized as a macro if called
              with arguments.

       e1 smallover e2
              As over, but reduces the type size of e1 and e2, and puts less
              vertical space between e1 and e2 and the fraction bar.  The over
              primitive corresponds to the TeX \over primitive in displayed
              equation styles; smallover corresponds to \over in non-display
              (“inline”) styles.

       space n
              Set extra vertical spacing around the equation, replacing the
              default values, where n is an integer in hundredths of an em.
              If positive, n increases vertical spacing before the equation;
              if negative, it does so after the equation.  This primitive
              provides an interface to groff's \x escape sequence, but with
              the opposite sign convention.  It has no effect if the equation
              is part of a pic(1) picture.

       special troff-macro e
              Construct an object by calling troff-macro on e.  The troff
              string 0s contains the eqn output for e, and the registers 0w,
              0h, 0d, 0skern, and 0skew the width, height, depth, subscript
              kern, and skew of e, respectively.  (The subscript kern of an
              object indicates how much a subscript on that object should be
              “tucked in”, or placed to the left relative to a non-subscripted
              glyph of the same size.  The skew of an object is how far to the
              right of the center of the object an accent over it should be
              placed.)  The macro must modify 0s so that it outputs the
              desired result, returns the drawing position to the text
              baseline at the beginning of e, and updates the foregoing
              registers to correspond to the new dimensions of the result.

              Suppose you want a construct that “cancels” an expression by
              drawing a diagonal line through it.

                     .de Ca
                     .  ds 0s \
                     \Z'\\*(0s'\
                     \v'\\n(0du'\
                     \D'l \\n(0wu -\\n(0hu-\\n(0du'\
                     \v'\\n(0hu'
                     ..
                     .EQ
                     special Ca "x \[mi] 3 \[pl] x" ~ 3
                     .EN

              We use the \[mi] and \[pl] special characters instead of + and -
              because they are part of the argument to a troff macro, so eqn
              does not transform them to mathematical glyphs for us.  Here's a
              more complicated construct that draws a box around an
              expression; the bottom of the box rests on the text baseline.
              We define the eqn macro box to wrap the call of the troff macro
              Bx.

                     .de Bx
                     .ds 0s \
                     \Z'\\h'1n'\\*[0s]'\
                     \v'\\n(0du+1n'\
                     \D'l \\n(0wu+2n 0'\
                     \D'l 0 -\\n(0hu-\\n(0du-2n'\
                     \D'l -\\n(0wu-2n 0'\
                     \D'l 0 \\n(0hu+\\n(0du+2n'\
                     \h'\\n(0wu+2n'
                     .nr 0w +2n
                     .nr 0d +1n
                     .nr 0h +1n
                     ..
                     .EQ
                     define box ' special Bx $1 '
                     box(foo) ~ "bar"
                     .EN

       split "text"
              As text, but since text is quoted, it is not subject to macro
              expansion; it is split up and the spacing between characters
              adjusted per subsection “Spacing and typeface” above.

       e1 uaccent e2
              Set e2 as an accent under e1.  e2 is assumed to be at the
              appropriate height for a letter without a descender;  eqn
              vertically shifts it depending on whether e1 has a descender.
              utilde is predefined using uaccent as a tilde accent below the
              baseline.

       undef name
              Remove definition of macro or primitive name, making it
              undefined.

       vcenter e
              Vertically center e about the math axis, a horizontal line upon
              which fraction bars and characters such as “+” and “−” are
              aligned.  MathML already behaves this way, so eqn ignores this
              primitive when producing that output format.  The built-in sum
              macro is defined as if by the following.

                     define sum ! { type "operator" vcenter size +5 \(*S } !

   Extended primitives
       GNU eqn extends the syntax of some AT&T eqn primitives, introducing one
       deliberate incompatibility.

       delim on
              eqn recognizes an “on” argument to the delim primitive
              specially, restoring any delimiters previously disabled with
              “delim off”.  If delimiters haven't been specified, neither
              command has effect.  Few eqn documents are expected to use “o”
              and “n” as left and right delimiters, respectively.  If yours
              does, consider swapping them, or select others.

       col n_{ ... }
       ccol n_{ ... }
       lcol n_{ ... }
       rcol n_{ ... }
       pile n_{ ... }
       cpile n_{ ... }
       lpile n_{ ... }
       rpile n_{ ... }
              The integer value n (in hundredths of an em) increases the
              vertical spacing between rows, using groff's \x escape sequence
              (the value has no effect in MathML mode).  Negative values are
              accepted but have no effect.  If more than one n occurs in a
              matrix or pile, the largest is used.

   Customization
       When eqn generates troff input, the appearance of equations is
       controlled by a large number of parameters.  They have no effect when
       generating MathML, which delegates typesetting to a MathML rendering
       engine.  Configure these parameters with the set primitive.

       set p n
              assigns parameter p the integer value n; n is interpreted in
              units of hundredths of an em unless otherwise stated.  For
              example,

                     set x_height 45

              says that eqn should assume that the font's x-height is
              0.45 ems.

              Available parameters are as follows; defaults are shown in
              parentheses.  We intend these descriptions to be expository
              rather than rigorous.

              minimum_size     sets a floor for the type size (in scaled
                               points) at which equations are set (5).

              fat_offset       The fat primitive emboldens an equation by
                               overprinting two copies of the equation
                               horizontally offset by this amount (4).  In
                               MathML mode, components to which fat_offset
                               applies instead use the following.
                                      <mstyle mathvariant='double-struck'>

              over_hang        A fraction bar is longer by twice this amount
                               than the maximum of the widths of the numerator
                               and denominator; in other words, it overhangs
                               the numerator and denominator by at least this
                               amount (0).

              accent_width     When bar or under is applied to a single
                               character, the line is this long (31).
                               Normally, bar or under produces a line whose
                               length is the width of the object to which it
                               applies; in the case of a single character,
                               this tends to produce a line that looks too
                               long.

              delimiter_factor Extensible delimiters produced with the left
                               and right primitives have a combined height and
                               depth of at least this many thousandths of
                               twice the maximum amount by which the sub-
                               equation that the delimiters enclose extends
                               away from the axis (900).

              delimiter_shortfall
                               Extensible delimiters produced with the left
                               and right primitives have a combined height and
                               depth not less than the difference of twice the
                               maximum amount by which the sub-equation that
                               the delimiters enclose extends away from the
                               axis and this amount (50).

              null_delimiter_space
                               This much horizontal space is inserted on each
                               side of a fraction (12).

              script_space     The width of subscripts and superscripts is
                               increased by this amount (5).

              thin_space       This amount of space is automatically inserted
                               after punctuation characters.  It also
                               configures the width of the space produced by
                               the ^ token (17).

              medium_space     This amount of space is automatically inserted
                               on either side of binary operators (22).

              thick_space      This amount of space is automatically inserted
                               on either side of relations.  It also
                               configures the width of the space produced by
                               the ~ token (28).

              x_height         The height of lowercase letters without
                               ascenders such as “x” (45).

              axis_height      The height above the baseline of the center of
                               characters such as “+” and “−” (26).  It is
                               important that this value is correct for the
                               font you are using.

              default_rule_thickness
                               This should be set to the thickness of the
                               \[ru] character, or the thickness of horizontal
                               lines produced with the \D escape sequence (4).

              num1             The over primitive shifts up the numerator by
                               at least this amount (70).

              num2             The smallover primitive shifts up the numerator
                               by at least this amount (36).

              denom1           The over primitive shifts down the denominator
                               by at least this amount (70).

              denom2           The smallover primitive shifts down the
                               denominator by at least this amount (36).

              sup1             Normally superscripts are shifted up by at
                               least this amount (42).

              sup2             Superscripts within superscripts or upper
                               limits or numerators of smallover fractions are
                               shifted up by at least this amount (37).
                               Conventionally, this is less than sup1.

              sup3             Superscripts within denominators or square
                               roots or subscripts or lower limits are shifted
                               up by at least this amount (28).
                               Conventionally, this is less than sup2.

              sub1             Subscripts are normally shifted down by at
                               least this amount (20).

              sub2             When there is both a subscript and a
                               superscript, the subscript is shifted down by
                               at least this amount (23).

              sup_drop         The baseline of a superscript is no more than
                               this much below the top of the object on which
                               the superscript is set (38).

              sub_drop         The baseline of a subscript is at least this
                               much below the bottom of the object on which
                               the subscript is set (5).

              big_op_spacing1  The baseline of an upper limit is at least this
                               much above the top of the object on which the
                               limit is set (11).

              big_op_spacing2  The baseline of a lower limit is at least this
                               much below the bottom of the object on which
                               the limit is set (17).

              big_op_spacing3  The bottom of an upper limit is at least this
                               much above the top of the object on which the
                               limit is set (20).

              big_op_spacing4  The top of a lower limit is at least this much
                               below the bottom of the object on which the
                               limit is set (60).

              big_op_spacing5  This much vertical space is added above and
                               below limits (10).

              baseline_sep     The baselines of the rows in a pile or matrix
                               are normally this far apart (140).  Usually
                               equal to the sum of num1 and denom1.

              shift_down       The midpoint between the top baseline and the
                               bottom baseline in a matrix or pile is shifted
                               down by this much from the axis (26).  Usually
                               equal to axis_height.

              column_sep       This much space is added between columns in a
                               matrix (100).

              matrix_side_sep  This much space is added at each side of a
                               matrix (17).

              draw_lines       If non-zero, eqn draws lines using the troff \D
                               escape sequence, rather than the \l escape
                               sequence and the \[ru] special character.  The
                               eqnrc file sets the default: 1 on ps, html, and
                               the X11 devices, otherwise 0.

              body_height      is the presumed height of an equation above the
                               text baseline; eqn adds any excess as extra
                               pre-vertical line spacing with troff's \x
                               escape sequence (85).

              body_depth       is the presumed depth of an equation below the
                               text baseline; eqn adds any excess as extra
                               post-vertical line spacing with troff's \x
                               escape sequence (35).

              nroff            If non-zero, then ndefine behaves like define
                               and tdefine is ignored, otherwise tdefine
                               behaves like define and ndefine is ignored.
                               The eqnrc file sets the default: 1 on ascii,
                               latin1, utf8, and cp1047 devices, otherwise 0.

   Macros
       In GNU eqn, macros can take arguments.  A word defined by any of the
       define, ndefine, or tdefine primitives followed immediately by a left
       parenthesis is treated as a parameterized macro call: subsequent tokens
       up to a matching right parenthesis are treated as comma-separated
       arguments.  In this context only, commas and parentheses also serve as
       token separators.  A macro argument is not terminated by a comma inside
       parentheses nested within it.  In a macro definition, $n, where n is
       between 1 and 9 inclusive, is replaced by the nth argument; if there
       are fewer than n arguments, it is replaced by nothing.

   Predefined macros
       GNU eqn supports the predefined macros offered by AT&T eqn: and,
       approx, arc, cos, cosh, del, det, dot, dotdot, dyad, exp, for, grad,
       half, hat, if, inter, Im, inf, int, lim, ln, log, max, min, nothing,
       partial, prime, prod, Re, sin, sinh, sum, tan, tanh, tilde, times,
       union, vec, ==, !=, +=, ->, <-, <<, >>, and “...”.  The lowercase
       classical Greek letters are available as alpha, beta, chi, delta,
       epsilon, eta, gamma, iota, kappa, lambda, mu, nu, omega, omicron, phi,
       pi, psi, rho, sigma, tau, theta, upsilon, xi, and zeta.  Spell them
       with an initial capital letter (Alpha) or in full capitals (ALPHA) to
       obtain uppercase forms.

       GNU eqn further defines the macros cdot, cdots, and utilde (all
       discussed above), dollar, which sets a dollar sign, and ldots, which
       sets an ellipsis on the text baseline.

   Fonts
       eqn uses up to three typefaces to set an equation: italic (oblique),
       roman (upright), and bold.  Assign each a groff typeface with the
       primitives gfont, grfont, and gbfont.  The defaults are the styles I,
       R, and B (applied to the current font family).  The chartype primitive
       (see above) sets a character's type, which determines the face used to
       set it.  The “letter” type is set in italics; others are set in roman.
       Use the bold primitive to select an (upright) bold style.

       gbfont f
              Select f as the bold font.  This is a GNU extension.

       gfont f
              Select f as the italic font.

       grfont f
              Select f as the roman font.  This is a GNU extension.

Options
       --help displays a usage message, while -v and --version show version
       information; all exit afterward.

       -C     Recognize .EQ and .EN even when followed by a character other
              than space or newline.

       -d xy  Specify delimiters x for left and y for right ends of equations
              not bracketed by .EQ/.EN.  x and y need not be distinct.  Any
              “delim xy” statements in the source file override this option.

       -f F   is equivalent to “gfont F”.

       -m n   is equivalent to “set minimum_size n”.

       -M dir Search dir for eqnrc before those listed in section
              “Description” above.

       -N     Prohibit newlines within delimiters.  This option allows eqn to
              recover better from missing closing delimiters.

       -p n   Set sub- and superscripts n points smaller than the surrounding
              text.  This option is deprecated.  eqn normally sets sub- and
              superscripts at 70% of the type size of the surrounding text.

       -r     Reduce the type size of subscripts at most once relative to the
              base type size for the equation.

       -R     Don't load eqnrc.

       -s n   is equivalent to “gsize n”.  This option is deprecated.

       -T dev Prepare output for the device dev.  In most cases, the effect of
              this is to define a macro dev with a value of 1; eqnrc uses this
              to provide definitions appropriate for the device.  However, if
              the specified driver is “MathML”, the output is MathML markup
              rather than troff input, and eqnrc is not loaded at all.  The
              default output device is ps.

Files
       /opt/homebrew/Cellar/groff/1.23.0_1/share/groff/1.23.0/tmac/eqnrc
              Initialization file.

MathML mode limitations
       MathML is designed on the assumption that it cannot know the exact
       physical characteristics of the media and devices on which it will be
       rendered.  It does not support control of motions and sizes to the same
       degree troff does.

       • eqn customization parameters have no effect on generated MathML.

       • The special, up, down, fwd, and back primitives cannot be
         implemented, and yield a MathML “<merror>” message instead.

       • The vcenter primitive is silently ignored, as centering on the math
         axis is the MathML default.

       • Characters that eqn sets extra large in troff mode—notably the
         integral sign—may appear too small and need to have their “<mstyle>”
         wrappers adjusted by hand.

       As in its troff mode, eqn in MathML mode leaves the .EQ and .EN tokens
       in place, but emits nothing corresponding to delim delimiters.  They
       can, however, be recognized as character sequences that begin with
       “<math>”, end with “</math>”, and do not cross line boundaries.

Caveats
       Tokens must be double-quoted in eqn input if they are not to be
       recognized as names of macros or primitives, or if they are to be
       interpreted by troff.  In particular, short ones, like “pi” and “PI”,
       can collide with troff identifiers.  For instance, the eqn command
       “gfont PI” does not select groff's Palatino italic font for the global
       italic face; you must use “gfont "PI"” instead.

       Delimited equations are set at the type size current at the beginning
       of the input line, not necessarily that immediately preceding the
       opening delimiter.

       Unlike TeX, eqn does not inherently distinguish displayed and inline
       equation styles; see the smallover primitive above.  However, macro
       packages frequently define EQ and EN macros such that the equation
       within is displayed.  These macros may accept arguments permitting the
       equation to be labeled or captioned; see the package's documentation.

Bugs
       eqn abuses terminology—its “equations” can be inequalities, bare
       expressions, or unintelligible gibberish.  But there's no changing it
       now.

       In nroff mode, lowercase Greek letters are rendered in roman instead of
       italic style.

       In MathML mode, the mark and lineup features don't work.  These could,
       in theory, be implemented with “<maligngroup>” elements.

       In MathML mode, each digit of a numeric literal gets a separate
       “<mn></mn>” pair, and decimal points are tagged with “<mo></mo>”.  This
       is allowed by the specification, but inefficient.

Examples
       We first illustrate eqn usage with a trigonometric identity.

              .EQ
              sin ( alpha + beta ) = sin alpha cos beta + cos alpha sin beta
              .EN

       It can be convenient to set up delimiters if mathematical content will
       appear frequently in running text.

              .EQ
              delim $$
              .EN
              Having cached a table of logarithms,
              the property $ln ( x y ) = ln x + ln y$ sped calculations.

       The quadratic formula illustrates use of fractions and radicals, and
       affords an opportunity to use the full space token ~.

              .EQ
              x = { - b ~ \[+-] ~ sqrt { b sup 2 - 4 a c } } over { 2 a }
              .EN

       Alternatively, we could define the plus-minus sign as a binary
       operator.  Automatic spacing puts 0.06 em less space on either side of
       the plus-minus than ~ does, this being the difference between the
       widths of the medium_space parameter used by binary operators and that
       of the full space.  Independently, we can define a macro “frac” for
       setting fractions.

              .EQ
              chartype "binary" \[+-]
              define frac ! { $1 } over { $2 } !
              x = frac(- b \[+-] sqrt { b sup 2 - 4 a c }, 2 a)
              .EN

See also
       “Typesetting Mathematics—User's Guide” (2nd edition), by Brian W.
       Kernighan and Lorinda L. Cherry, 1978, AT&T Bell Laboratories Computing
       Science Technical Report No. 17.

       The_TeXbook, by Donald E. Knuth, 1984, Addison-Wesley Professional.
       Appendix G discusses many of the parameters from section
       “Customization” above in greater detail.

       groff_char(7), particularly subsections “Logical symbols”,
       “Mathematical symbols”, and “Greek glyphs”, documents a variety of
       special character escape sequences useful in mathematical typesetting.

       groff(1), troff(1), pic(1), groff_font(5)

groff 1.23.0                      5 July 2023                           eqn(1)