<html><head><meta name="color-scheme" content="light dark"></head><body><pre style="word-wrap: break-word; white-space: pre-wrap;">%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 7-4-21 on page 493.
%% 
%%  Copyright (C) 2007 Michel Goossens, Frank Mittelbach, Denis Roegel, Sebastian Rahtz, Herbert Vo\ss 
%% 
%%  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{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{207.83385pt}
\StartShownPreambleCommands
\usepackage[all,2cell]{xy}
\StopShownPreambleCommands
\begin{document}
\UseAllTwocells
\[
\xymatrix @=15mm {
  L_1 \rlowertwocell&lt;-3&gt;_{a_1}{&lt;-1&gt;}
      \rcompositemap&lt;6&gt;_{a_2}^{a_3}{\omit}
&amp; R_1 \dtwocell&lt;0&gt;_{a_4}{"}
\\ L_2 \uuppertwocell_u^d{\omit}
       \rtwocell&lt;2&gt;{'id}
&amp;  R_2
 }\]
\end{document}
</pre></body></html>