[help-texinfo] Typing rules in Texinfo manual

[Stefan Monnier]

I'm working on a new (academic) language and would like to write its doc
in Texinfo, but part of the doc should be formal typing rules, which are
traditionally typeset in LaTeX with things like \frac (or other ways to
get similar "derivation rules").  What would be my best option in
Texinfo?  I can't see anything like @frac so it seems that I might be
stuck with writing separate things for the various PDF/Info/HTML
outputs, which I'd rather avoid.

In Info, I'd like to be able to get things that look like:

     Env |- Exp1 : Type1            Env |- Exp2 : Type2
     --------------------------------------------------
                 Env |- Exp3 : Type3

What do you think would be the least painful way to write
this in Texinfo?


        Stefan