%% 
%%  Ein Beispiel der DANTE-Edition
%%  Mathematiksatz mit LaTeX
%%  3. Auflage
%%  Beispiel 09-26-1 auf Seite 207.
%%  Copyright (C) 2018 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[10pt]{exaartplain}
\pagestyle{empty}
\setlength\textwidth{170.40707pt}
\AtBeginDocument{\setlength\parindent{0pt}}
%StartShownPreambleCommands
\usepackage{witharrows}
%StopShownPreambleCommands
\begin{document}
$\begin{WithArrows}
A &= \bigl((a+b)+1\bigr)^2\Arrow{}\Arrow{}[jump=2]\\
  &= (a+b)^2 + 2(a+b) +1 \\
  &= a^2 + 2ab + b^2 + 2a + 2b +1
\end{WithArrows}$
\end{document}