eqn(1)

💖 Name 💖

okay so bestie, this is eqn(1) — format mathematics (equations) for groff or MathML. That's the whole vibe: equations get formatted, and this page is your group-chat explainer. 💅

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✨ Synopsis ✨

Here's the exact invocation tea, no cap:

eqn [-CNrR] [-d xy] [-f global-italic-font] [-m minimum-type-size]
    [-M eqnrc-directory] [-p super/subscript-size-reduction] [-s global-
type-size] [-T device] [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 <hotpink>troff(1) preprocessor</hotpink>: it translates expressions written in its own language, embedded inside roff(7) input, 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 run directly by you, bestie — it gets invoked by specifying the -e option to groff(1). And while GNU eqn's input syntax is highly compatible with AT&T eqn, the output eqn produces <purple>cannot</purple> be processed by AT&T troff; GNU troff (or a troff implementing the relevant GNU extensions) must be used. If no file operands are present, 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 /usr/share/groff/site-tmac, and finally in the standard macro directory /usr/share/groff/1.24.2/tmac. If it exists and is readable, eqn processes it before any input. (Yes, that's <lavender>three places</lavender>, in that exact order — write it down. ✨)

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. Four points are worth 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.
• GNU eqn's delim primitive does not treat an on argument as a pair of equation delimiters.

🦋 Anatomy of an equation 🦋

eqn input consists of <cyan>tokens</cyan>. Consider a form of Newton's second law of motion for constant mass. The input

.EQ
F =
m a
.EN

becomes F=ma. 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.

Beyond their primary functions, the following input characters separate tokens as well.

• { } — Braces perform <mint>grouping</mint>. 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.
• ^ ~ — These are the half space and full space, respectively. Use them to tune the appearance of the output.
• Tab and leader characters — They separate tokens as well as advance the drawing position to the next tab stop, but they 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 (gifont and gsize), or declaring or deleting macros (define and undef); these are termed <peach>commands</peach>. Other primitives perform formatting operations on the tokens around 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 used together as 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 a type to each equation component, adjusting the space around it accordingly. Recognized types follow; 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, <green>persistently</green>.

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 🌈

We describe the GNU extension primitives type and chartype in subsection “Spacing and typeface” above; set and reset in subsection “Customization” below; and gbfont, gifont, and grfont 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. eqn assumes that e2 is at the appropriate height for a lowercase letter without an ascender, and shifts it vertically based on e1's height. For example, eqn defines hat as follows.

accent { roman "^" }

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. 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 reduce the type size of e1 and e2, and put 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 🌸

okay so this one is a whole vibe — you're literally teaching eqn a brand new trick by handing it off to a troff macro. Construct an object by calling troff-macro on e. Here's the tea: the troff string 0s contains the eqn output for e, and the registers 0w, 0h, 0d, 0skern, and 0skew hold the width, height, depth, subscript kern, and skew of e, respectively. 🫶

And because I know you're gonna ask what even is a subscript kern — it's 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. Skew is how far to the right of the center of the object an accent over it should be placed. Slay, now you know. 💅

So your macro has chores, bestie, and they are non-negotiable: it must modify 0s so that it outputs the desired result, return the drawing position to the text baseline at the beginning of e, and update the foregoing registers to correspond to the new dimensions of the result. That's the whole assignment. 👑

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

Not me using \[mi] and \[pl] special characters instead of + and - — and there's a reason, okay? Because they're part of the argument to a troff macro, so eqn does not transform them to mathematical glyphs for us. ikyk. 😭

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" 🦋

Literally just like 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. That's it, that's the whole thing. ✨

💜 e1 uaccent e2 💜

Set e2 as an accent under e1. Under, bestie, under. 🙈 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. And utilde is predefined using uaccent as a tilde accent below the baseline. Cute.

🎀 undef name 🎀

Remove definition of macro or primitive name, making it undefined. Gone. Poof. Not me erasing things from existence. 💀

⭐ vcenter e ⭐

Vertically center e about the math axis — that's the 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 (MathML said "I got this already" 💅). The built-in sum macro is defined as if by the following:

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

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🌈 Extended primitives 🌈

GNU eqn extends the syntax of some AT&T eqn primitives, introducing one deliberate incompatibility. One! We love a heads-up. 👑

🌸 delim on 🌸

GNU 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. So if yours does… swap them, or select others. 🙈

fr fr just swap them. don't fight it.

💅 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, uses the formatter's \x escape sequence to increase the vertical spacing between rows; eqn ignores it when producing MathML. Negative values are accepted but have no effect (sorry, they just don't do anything, they're just there existing 😭). If more than one n occurs in a matrix or pile, the largest is used. Biggest wins. periodt.

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🎀 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 and reset primitives. 🫶

✨ Setting and resetting ✨

• 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.

• reset p — restores the default value of parameter p.

Available parameters p are as follows; defaults are shown in parentheses. We intend these descriptions to be expository rather than rigorous — so like, vibes-based documentation, basically. 😌

• 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). When producing MathML output, 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. (Aesthetic crisis avoided 🎀)
• 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 (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 (28).
• half_space — configures the width of the space produced by the ^ token (17).
• full_space — 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. No cap, get this one right. 👑
• 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. (smaller number, smaller shift, we keep the hierarchy 💅)
• 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).

still in the parameter list, bestie — don’t worry, every single knob gets its moment 💅

• 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, and utf8 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 (heavy). Assign each a groff typeface with the GNU extension primitives grfont, gifont, and gbfont. The defaults are the styles R, I, 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.
• gifont f — select f as the italic font. GNU eqn recognizes gfont as a synonym for AT&T compatibility.
• grfont f — select f as the roman font.

🦋 roff interface 🦋

The string 10 stores the most recently formatted equation. The register MK stores the horizontal drawing position of the most recently assigned mark. Avoid using these names for any other purpose.

GNU eqn internally employs register, string, macro, and diversion names beginning with the numeral 0. (AT&T eqn used identifiers starting with the numeral 1.) A document to be preprocessed with GNU eqn should not use any such identifiers.

💅 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 gifont 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, allowing 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 super- and subscripts at most once relative to the base type size.
• -R — don’t load eqnrc.
• -s n — is equivalent to gsize n. This option is deprecated.
• -T dev — prepare output for the device dev. This option defines a macro dev with the value 1; eqnrc thereby provides definitions appropriate to the device. However, if dev is “MathML”, eqn produces output in that language rather than roff, and does not load eqnrc. The default device is ps.

deprecated alert 💅: -p and -s are literally called deprecated in the manual — that’s not me being dramatic, that’s the source.

🌸 Exit status 🌸

eqn exits with status 0 on successful operation, status 2 if the program cannot interpret its command-line arguments, and status 1 if it encounters an error during operation.

🎀 Files 🎀

/usr/share/groff/1.24.2/tmac/eqnrc — initializes the preprocessor for troff output. Any valid eqn input is accepted.

😭 MathML output limitations 😭

MathML’s design assumes 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.

• GNU eqn’s rendering parameters (see section “Customization” above) 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 output — notably the integral sign — may appear too small and need to have their <mstyle> wrappers adjusted by hand.

As when producing troff output, eqn generates MathML that 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 gifont PI does not select the gropdf(1) or grops(1) device’s Palatino italic font as the global italic face; you must use gifont "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.

When producing terminal output, GNU eqn renders lowercase Greek letters in roman instead of italic style.

When producing MathML output, the mark and lineup features don’t work. These could, in theory, be implemented with <maligngroup> elements.

When producing MathML output, 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 🌸

Okay bestie, this is the part where we actually do stuff — like, theory is cute but watch and learn 💅

Example one: a trig identity, we're so back

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

That's it, that's the whole vibe. Trig identity, served fresh ✨

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Example two: delimiters, because typing .EQ every five seconds is giving tired

Lowkey it can be convenient to set up delimiters if mathematical content is gonna appear frequently in running text — like, actually often, not just once 🎀

.EQ
delim $$
.EN

Then, having cached a table of logarithms, the property $ln ( x y ) = ln x + ln y$ sped calculations. Iconic. The $…$ is doing all the work and nobody's even thanking it 😭

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Example three: the quadratic formula, come get your fractions and radicals

This one's a whole opportunity to flex fractions, radicals, and the full space token ~. Obsessed with the multitasking honestly 🦋

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

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Example four: define your own operators and macros, main character behavior

Alternatively — yes, there's an alternatively, we're eating good today 🍓 — we could define the plus-minus sign as a binary operator.

Heads up, the spacing math is real, so pay attention: automatic spacing puts 0.06 em less space on either side of the plus-minus than ~ does. Why? Because that's the difference between the widths of the medium_space parameter used by binary operators and that of the full space. Numbers don't lie, bestie 💀

Independently (separate thing, not related, don't @ me), we can define a macro frac for setting fractions. Look at this:

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

$1 and $2 are your arguments, !…! is your macro delimiter situation — and boom, custom frac, no cap 🔥

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👑 SEE ALSO 👑

Reading list time, bestie. Yes we're citing sources, we're academic like that 📚✨

• "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 original icon, the blueprint, we stan 🫶
• The TeXbook, by Donald E. Knuth, 1984, Addison-Wesley Professional. — specifically Appendix G, which discusses many of the parameters from the "Customization" section above in greater detail. Like, more detail than we gave you. Go off, Don 💜
• groff_char(7) — documents a variety of special character escape sequences that are useful in mathematical typesetting. Check the subsections "Logical symbols", "Mathematical symbols", and "Greek glyphs" in particular — those three are the 🌈 moment 🌈
• groff(1), troff(1), pic(1), groff_font(5) — the rest of the friend group, go say hi 💖

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And that's a wrap on the whole page, bestie! 🎀 This little manual is groff 1.24.2, dated 2026-10-01 — so go forth, typeset some math, be the math girlie you were always meant to be 💅✨