%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 6-2-67 on page 363.
%% 
%%  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{159.83385pt}
\setlength\parindent{0pt}
\StartShownPreambleCommands
\usepackage{pstricks,pst-node}
\StopShownPreambleCommands
\begin{document}
$\begin{psmatrix}[mnode=dia,colsep=1cm]
   & [mnode=circle] X \\  Y & Z
 \end{psmatrix}
 \psset{nodesep=3pt,arrows=->}
 \ncline{1,2}{2,1} \ncline{1,2}{2,2}
 \ncline[linestyle=dotted]{2,1}{2,2} $
\end{document}
