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<span
class="cmbx-10">Any explanation for the following problem? </span>The native LaTeX compiler has no problem with examples 1
and 2. On example 3 it complains: ‘<span
class="cmtt-10">Argument of \xhalign has an extra }</span>’. When compiled in isolation,
examples 2 and 3 produce the same tracing until <span
class="cmtt-10">\xhalign </span>is invoked.
<div class="Verbatim"><span
class="cmtt-10"> </span><span
class="cmtt-10"> \tracingcommands=2</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> \tracingmacros=2</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">\documentclass{article}</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">\begin{document}</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">\catcode‘\@=11</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">\def\eqnarray{%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \stepcounter{equation}%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \def\@currentlabel{\p@equation\theequation}%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \global\@eqnswtrue</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \m@th</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \global\@eqcnt\z@</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \tabskip\@centering</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \let\\\@eqncr</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> $$\everycr{}\xhalign</span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \cr</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">}</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">\def\xhalign#1\cr{%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \halign</span><span
class="cmtt-10"> to\displaywidth\bgroup</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \hskip\@centering$\displaystyle\tabskip\z@skip{##}$\@eqnsel</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> &\global\@eqcnt\@ne\hskip</span><span
class="cmtt-10"> \tw@\arraycolsep</span><span
class="cmtt-10"> \hfil${##}$\hfil</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> &\global\@eqcnt\tw@</span><span
class="cmtt-10"> \hskip</span><span
class="cmtt-10"> \tw@\arraycolsep</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> $\displaystyle{##}$\hfil\tabskip\@centering</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> &\global\@eqcnt\thr@@</span><span
class="cmtt-10"> \hb@xt@\z@\bgroup\hss##\egroup</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \tabskip\z@skip</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \cr</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">}</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> \vbox\bgroup</span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> %%</span><span
class="cmtt-10"> example</span><span
class="cmtt-10"> 1</span><span
class="cmtt-10"> %%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \begin{eqnarray}</span><span
class="cmtt-10"> </span><span
class="cmtt-10"> x</span><span
class="cmtt-10"> \end{eqnarray}%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> \egroup</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> \begin{tabular}{c}</span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> %%</span><span
class="cmtt-10"> example</span><span
class="cmtt-10"> 2</span><span
class="cmtt-10"> %%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \vbox{%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \begin{eqnarray}</span><span
class="cmtt-10"> </span><span
class="cmtt-10"> x</span><span
class="cmtt-10"> \end{eqnarray}%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> }%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> \end{tabular}</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> \begin{tabular}{c}</span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> %%</span><span
class="cmtt-10"> example</span><span
class="cmtt-10"> 3</span><span
class="cmtt-10"> %%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \vbox\bgroup</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \begin{eqnarray}</span><span
class="cmtt-10"> </span><span
class="cmtt-10"> x</span><span
class="cmtt-10"> \end{eqnarray}%</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> </span><span
class="cmtt-10"> \egroup</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span><span
class="cmtt-10"> \end{tabular}</span><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10"> </span>
<br /><span
class="cmtt-10">\end{document}</span><span
class="cmtt-10"> </span>
<br /></div>
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