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%%  An UIT Edition example
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%%  Example 10-02-1 on page 200.
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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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\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\AtBeginDocument{\setlength\parindent{0pt}}
\setcounter{equation}{0}
\renewcommand\theequation{10.\arabic{equation}}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
\begin{equation}\addtolength{\arraycolsep}{-3pt}
I(z)=\delta_{0}\left\{\begin{array}{lcrcl}
 D+z & \quad & -D & \le z\le & -p\\
 D-\frac{1}{2}\left(p-\frac{z^{2}}{p}\right)
     & \quad & -p & \le z\le & \phantom{-}p\\
 D-z & \quad & p & \le z\le & \phantom{-}D
\end{array}\right.
\end{equation}
\end{document}