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%%  Ein Beispiel der DANTE-Edition
%%  Mathematiksatz mit LaTeX
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%%  Beispiel 04-05-10 auf Seite 44.
%%  Copyright (C) 2018 Herbert Voss
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\documentclass[10pt]{screxa}
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\begin{document}
\begin{equation}
\mathcal{W} := \left\{ \bigcup^{\infty}_{j=0} W_j \; \middle| \;
  W_j \subset \tilde P_{*j} \textrm{ offen},\; W_j \subset W_{j+1}\right\}
\end{equation}
\end{document}