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%%  Ein Beispiel der DANTE-Edition
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%%  1. Auflage
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%%  Beispiel 09-07-47 auf Seite 462.
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%%  Copyright (C) 2011 Herbert Voss
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%%  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.
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%%  See http://www.latex-project.org/lppl.txt for details.
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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{190.324pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{63}
\renewcommand\theequation{9.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{subequations}
\renewcommand{\theequation}{%
  \theparentequation -\arabic{equation}}
\begin{align}
y &= d\\
y &= cx+d\label{eq:subequation}\\
y &= bx^{2}+cx+d\\
y &= ax^{3}+bx^{2}+cx+d
\end{align}
\end{subequations}
Eine Referenz zu Gl.~\ref{eq:subequation}
  auf S.~\pageref{eq:subequation}.
\end{document}