Re: Texinfo TeX accepts LaTeX math, how?

[Gavin Smith]

On Mon, Oct 26, 2020 at 11:58:56AM +0100, Patrice Dumas wrote:
> Hello,
> 
> Surprisingly (for me), the @displaymath example in the Texinfo manual
> works when producing a pdf using texi2dvi.  However, it uses \frac{}{},
> which is not not a plain TeX construct, as far as I know.  How is that
> possible?  If the math in Texinfo is "LaTeX math" it is much simpler for
> writers, as "plain TeX math" is less known that "LaTeX math" but also
> for math rendering in HTML, as it means that latex2html can be used
> without trouble and htlatex can be used instead of httex.

I added \frac to texinfo.tex very recently as it is easy to implement
and probably the most missed LaTeX command by far.  However, it could
be confusing to use in the manual as it wouldn't get over that plain
TeX should be used.

> If it is not the same as LaTeX math, but a superset of plain TeX math,
> could you tell me how I can modify the TeX file produced by tex4ht.pm
> for httex such that there is support of the same constructs in math
> rendering through tex4ht?  Right now, \frac appears as undefined when
> processing with httex.

In that case it would be simpler just to use \over in the example.
Another option is to use htlatex instead (if there is such a program),
but that could be problematic if there are any important usages of
plain TeX that don't work with LaTeX.