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%% An UIT Edition example
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%% Example 10-09-10 on page 220.
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%% Copyright (C) 2010 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.
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% Show page(s) 1
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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{31}
\renewcommand\theequation{10.\arabic{equation}}
\StartShownPreambleCommands
\usepackage{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{align}
\sum_{i=1}^\infty \frac{1}{i} &= 1+\frac{1}{2}+\frac{1}{3}+\frac{1}{4}
+\frac{1}{5}+\frac{1}{6}+\frac{1}{7}+\frac{1}{8}+\frac{1}{9}
+\cdots+\frac{1}{16}+\cdots\\
& \ge 1+\frac{1}{2}+\underbrace{\frac{1}{4}+\frac{1}{4}}_{\frac{1}{2}}
+\underbrace{\frac{1}{8}+\frac{1}{8}+\frac{1}{8}+\frac{1}{8}}_{\frac{1}{2}}
+\underbrace{\frac{1}{16}+\cdots+\frac{1}{16}}_{\frac{1}{2}}+\cdots\\
&= 1+\frac{1}{2}+\frac{1}{2}+\frac{1}{2}+\frac{1}{2}+\cdots\to\infty
\quad\rule{1ex}{1ex}
\end{align}
\end{document}
