%%
%% The LaTeX Companion, 2ed (second printing August 2004)
%%
%% Example 8-3-6 on page 488.
%%
%% 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{ttctexa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{207.0pt}

\StartShownPreambleCommands
\usepackage{amsmath,amscd}
\DeclareMathOperator\add{add}
\DeclareMathOperator\cf {cf}
\DeclareMathOperator\cov{cov}
\DeclareMathOperator\non{non}
\StopShownPreambleCommands
\begin{document}
\[ \begin{CD}
     \cov (L) @>>> \non (K) @>>> \cf (K)  \\
       @VVV          @AAA          @AAA   \\
     \add (L) @>>> \add (K) @>>> \cov (K) \\
   \end{CD} \]
\end{document}