%% An UIT Edition example

%%
%% An UIT Edition example
%%
%% Example 06-11-9 on page 108.
%%
%% Copyright (C) 2010 Herbert Voss
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3
%% of this license or (at your option) any later version.
%%
%% See http://www.latex-project.org/lppl.txt for details.
%%
%%
%% ====
% Show page(s) 1
%%
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{59}
\renewcommand\theequation{6.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath} \newcounter{mySubCounter}
\newcommand\twocoleqn[2]{\setcounter{mySubCounter}{0}\let\OldTheEq\theequation%
\renewcommand\theequation{\OldTheEq\alph{mySubCounter}}%
\noindent\begin{minipage}{.49\textwidth}
\begin{align}\refstepcounter{mySubCounter}#1\end{align}
\end{minipage}\hfill\addtocounter{equation}{-1}%
\begin{minipage}{.49\textwidth}
\begin{align}\refstepcounter{mySubCounter}#2\end{align}
\end{minipage}\let\theequation\OldTheEq}
\StopShownPreambleCommands
\begin{document}
\twocoleqn{y=f(x)}{y=f(z)}
\begin{align} z &= f(x,y) \end{align}
\end{document}