%% 
%%  Ein Beispiel der DANTE-Edition
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%%  1. Auflage
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%%  Beispiel 09-07-25 auf Seite 451.
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%%  Copyright (C) 2011 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.
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% Show page(s) 1
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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{166.324pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{48}
\renewcommand\theequation{9.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{align} \begin{bmatrix}
  a & b\\
  \begin{Vmatrix} A & B\\ C & D \end{Vmatrix}
  c & d
\end{bmatrix} \end{align}
\end{document}
