%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-2-39 on page II-152 in "Fine-tuning tag placement".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See
https://www.latex-project.org/lppl.txt for details.
%%
\documentclass{tlc3examargin}
\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}
