%% 
%%  An UIT Edition example
%% 
%%  Example 04-01-6 on page 34.
%% 
%%  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
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{375.57637pt}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\setcounter{equation}{4}
\renewcommand\theequation{4.\arabic{equation}}
\AtBeginDocument{\setlength\parindent{0pt}}
\StartShownPreambleCommands

\StopShownPreambleCommands
\begin{document}
\begin{equation}
x = \left\{
  \begin{array}{ l p{0.7\textwidth} }
    0 & if A=\ldots\tabularnewline
    1 & if B=\ldots\tabularnewline
    x & \parbox[t]{0.75\columnwidth}{This text can be as long as you want it
    to be, and now it will even wrap onto several lines because of the
    \texttt{\textbackslash parbox} used. Isn't that nice. After all it doesn't
    look good if the text protrudes into the margin like it did before.}
  \end{array}
  \right.
\end{equation}
\end{document}