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%%  Ein Beispiel der DANTE-Edition
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%%  2. Auflage
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%%  Beispiel 09-07-62 auf Seite 445.
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%%  Copyright (C) 2016 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}}
\setcounter{equation}{73}
\renewcommand\theequation{9.\arabic{equation}}
%StartShownPreambleCommands
\usepackage{amsmath}
\newcommand*\diff{\mathop{}\!\mathrm{d}}
%StopShownPreambleCommands
\begin{document}
$a\boxed{b+c}$
\begin{align}
         f(x) = \int_1^{\infty}\frac{1}{x^2}\diff t = 1\\
  \boxed{f(x) = \int_1^{\infty}\frac{1}{x^4}\diff t = \frac{1}{3}}
\end{align}
\end{document}