[luatex] How to get a \mid binary relation that grows in LuaTeX

[David Carlisle]

Hans wrote

> sure but then, using an empty \mathrel{} in there is kind of bad

It's possibly the only way in classic etex to define a version of
\middle that gives \mathrel space

\def\relmiddle#1{\mathrel{}\middle#1\mathrel{}} ... \rmiddle | ...

acts like a relation with respect to automatic muskips on both sides


> .. better add some explicit muskip then

you can't classically detect what \muskip needs adding unfortunately...


so \Umiddle is (of course:-) a whole lot better (apart from the
confusing numbering scheme:-) but
the \mathrel{}\middle|\mathrel{} idiom is likely to be quite common in
legacy documents moving to luatex


David