%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-2-3 on page II-133 in "Comparison of amsmath/mathtools with \protect \slatex ".
%%
%% 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}

  % Shorten the vertical size of the example ...
  \AtBeginDocument{%
    \setlength\abovedisplayskip{.5\abovedisplayskip}%
    \setlength\belowdisplayskip{.5\belowdisplayskip}%
  }

%StartShownPreambleCommands
\usepackage{amsmath}
%StopShownPreambleCommands

\begin{document}
\begin{equation}
  x^2 + y^2  =  z^2
\end{equation}
\begin{align}
  x^2 + y^2 &=  z^2 \\ x^3 + y^3 &<  z^3
\end{align}
\begin{eqnarray}
  x^2 + y^2 &=& z^2 \\ x^3 + y^3 &<& z^3
\end{eqnarray}
\end{document}