%% 
%%  Ein Beispiel der DANTE-Edition
%%  
%%  1. Auflage
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%%  Beispiel 09-08-11 auf Seite 478.
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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.
%% 
%% 
%% ==== 
% Show page(s) 1
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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{190.324pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands
\usepackage{amsmath,cancel}
\StopShownPreambleCommands
\begin{document}
$f(x)=\dfrac{\left(x^2+1\right)
  \cancelto{1}{(x-1)}}{%
    \cancelto{1}{(x-1)}\kern1em(x+1)}$
\end{document}