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%%  Ein Beispiel der DANTE-Edition
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%%  Beispiel 09-06-49 auf Seite 438.
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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{352.81416pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands
\newcommand*\diff{\mathop{}\!\mathrm{d}}
\StopShownPreambleCommands
\begin{document}
\[ ay^\prime=a\frac{\diff y}{\diff x} \quad c\cdot v =  c\,\frac{\diff s}{\diff t} \quad
  a = \frac{\diff{^2t}}{\diff{t^2}} \quad \int\!\!\diff y=\int\!\sin(x)\diff x \]
\end{document}