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%%  Example 02-01-2 
%%  Copyright (C) 2016 Herbert Voss
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\documentclass[]{screxa}
\pagestyle{empty}
\setlength\textwidth{158.31393pt}
\setlength\parindent{0pt}
%StartShownPreambleCommands
\usepackage{amsmath}
%StopShownPreambleCommands
\begin{document}
\begin{align}
  y      &= d\label{eq:align}\\
  y      &= cx+d\\
  y_{12} &= bx^{2}+cx+d\\
  y(x)   &= ax^{3}+bx^{2}+cx+d
\end{align}
See eq.~\ref{eq:align} \ldots
\end{document}
