%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 8-2-28 on page 484.
%%
%% Copyright (C) 2004 Frank Mittelbach, Michel Goossens,
%%    Johannes Braams, David Carlisle, and Chris Rowley
%%
%% 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.
%%

\documentclass{ttctexamargin}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{183.0pt}

\StartShownPreambleCommands
\usepackage[leqno]{amsmath}
\StopShownPreambleCommands
\begin{document}
\begin{gather}   \raisetag{-10pt}
  \text{The sign function: \ }
     \mathcal{S}(x) =  \begin{cases}
                         -1   &  x < 0 \\
                          0   &  x = 0 \\
                          1   &  x > 0
                       \end{cases}
\end{gather}
\end{document}
