%%
%% The LaTeX Companion, 3ed
%%
%% Example 11-4-3 on page II-164 in "amsmath, mathtools, extarrows --- Decorated arrows".
%%
%% 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{135.0pt}

%StartShownPreambleCommands
\usepackage{mathtools,extarrows}
%StopShownPreambleCommands

\begin{document}
\begin{gather}
  A \xlongequal      [\text{characters}]{ +12 }
  M \xLongrightarrow [\text{characters}]{\text{more}} Z \\
  0 \xrightarrow{x} \epsilon  \xlongrightarrow{x} 1     \\
  \xLongleftarrow{1} \xLongrightarrow{2} \xlongleftarrow{3}
  \xlongrightarrow{4} \xlongleftrightarrow{5}
\end{gather}
\end{document}