%% 
%%  An UIT Edition example
%% 
%%  Example 04-13-1 on page 62.
%% 
%%  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.
%% 
%% 
%% ==== 
% Show page(s) 1
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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands
\newcommand*\diff{\mathop{}\!\mathrm{d}}
\StopShownPreambleCommands
\begin{document}
\[ \oint_{U(r)}H\diff r=\ointop_{U(r)}H\diff r=\frac{I}{2\pi r_0}\oint_{U(r)}
   \diff r=\frac{I}{2\pi r_0}\oint_{U(r)}\diff r=I \]
\end{document}