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%%  Ein Beispiel der DANTE-Edition
%%  Mathematiksatz mit LaTeX
%%  3. Auflage
%%  Beispiel 06-12-10 auf Seite 121.
%%  Copyright (C) 2018 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
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\setlength\textwidth{352.81416pt}
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\begin{document}
\begin{align}
\prod_{j\ge0}\biggl(\sum_{k\ge0}a_{jk}z^k\biggr) = \sum_{n\ge0}z^n\,
  \Biggl(\sum_{\substack{k_0,k_1,\ldots\ge0\\k_0+k_1+\cdots=n}}
  a_{0k_0}a_{1k_1}\ldots\,\Biggr)
\end{align}
\end{document}