% eqnarray environment
% Paul Taylor, 11 June 2003

% By default, LaTeX's eqnarray environment has three columns (left, centre,
% right) and adds an equation number on the right against the margin. The
% following modified form of it is compatible, but if there is a fourth
% column it is set in text mode in place of the equation.

\def\eqnarray{$$\global\@eqnswtrue\global\@eqcnt\z@\let\\=\@eqncr
\tabskip\@centering
\WillHandleQED
\halign to \linewidth\bgroup
   \@eqnsel$\displaystyle\tabskip\z@{##}$\hskip\@centering&%
   \global\@eqcnt\@ne\hskip2\arraycolsep \hfil${##}$\hfil&%
   \global\@eqcnt\tw@\hskip2\arraycolsep
        $\displaystyle\tabskip\z@{##}$\hfil\tabskip\@centering&%
   \global\@eqcnt\thr@@\hbox to\z@\bgroup\hss##\tabskip\z@\cr}

\def\@@eqncr{%
\let\@tempa\relax
\ifcase\@eqcnt
        \def\@tempa{& & &}%
\or     \def\@tempa{& &}%
\or     \def\@tempa{&}%
\else   \@eqnswfalse
\fi 
\@tempa
\if@eqnsw
        \@eqnnum\stepcounter{equation}%
\fi
\HandleQED
\egroup % matches \bgroup in fourth cell of preamble
\global\@eqnswtrue
\global\@eqcnt\z@
\cr}