Re: Bug#264394: tetex-bin: e-TeX is broken on registers > 255

[Richard Lewis <debian@rtf.org.uk>]

Benjamin BAYART <bayartb@edgard.fdn.fr> writes:

> Here is a minimal example (amsmath is required to show the bug):
>
> \documentclass{article}
>
> \usepackage{amsmath}
>
> \begin{document}
>
> \makeatletter
> \dimendef\z@=263\relax
> \z@=0pt\relax
> \[aa\]
> \show\z@
>
> \end{document}
>

I'm not sure why you'd want to change \z@, but...

If you add the following to the preamble (it's the definition from
amsmeth.sty except for the added \show\z@'s) you can see that \z@
changes definition when the closing `$$' is executed. 

\def\endmathdisplay#1{%
  \ifmmode \else \@badmath \fi
  \endmathdisplay@a
\show\z@ % \z@ is still \dimen263
  $$%
\show\z@ % \z@ is now \count652
  \global\let\df@label\@empty \global\let\df@tag\@empty
  \global\tag@false \global\let\alt@tag\@empty
  \global\@eqnswfalse
}

(Just saying

\dimendef\z@263
\z@=0pt

$$ a $$
\show\z@

produces no error, so the bug is somewhat complicated...)