breqn

Different ways to keep a bit of glue from disappearing at the beginning of a line
after line breaking:
• Zero-thickness rule
• Null character
• \vadjust{} (The TEXbook, Exercise ??)
The null character idea would be nice except it creates a mathord which then
screws up math spacing for e.g., a following unary minus sign. (the vrule is transparent
to the math spacing). The vadjust is the cheapest in terms of box memory—it
vanishes after the pass through TEX’s paragrapher. It is what I would have
used, except that the equation contents get run through two paragraphing passes,
once for breaking up LR boxes and once for the real typesetting. If \keep@glue
were done with an empty vadjust, it would disappear after the first pass and—in
particular—the pre-bin-op adjustment for relation symbols would disappear at a
line break.
84 \def\keep@glue{\z@rule\relax}
\replicate This is a fully expandable way of making N copies of a token list. Based on a post
of David Kastrup to comp.text.tex circa January 1999. The extra application of
\number is needed for maximal robustness in case the repeat count N is given in
some weird TEX form such as "E9 or \count9.
\replicate@a
\8m fix
\8q fix
85 % usage: \message{H\replicate{5}{i h}ow de doo dee!}
86 \begingroup \catcode‘\&=11
87 \gdef\replicate#1{%
88 \csname &\expandafter\replicate@a\romannumeral\number\number#1 000q\endcsname
89 }
90 \endgroup
91 \long\def\replicate@a#1#2\endcsname#3{#1\endcsname{#3}#2}
92 \begingroup \catcode‘\&=11
93 \long\gdef\&m#1#2{#1\csname &#2\endcsname{#1}}
94 \endgroup
95 \@xp\let\csname\string &q\endcsname\@gobble
\mathchars@reset Need to patch up this function from flexisym a little, to better handle certain
constructed symbols like \neq.
96 \ExplSyntaxOn
97 \g@addto@macro\mathchars@reset{%
98 %\let\@symRel\@secondoftwo \let\@symBin\@secondoftwo
99 %\let\@symDeL\@secondoftwo \let\@symDeR\@secondoftwo
20