%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 6-2-52 on page 356.
%% 
%%  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}
\cnode(0.5,0){.25cm}{root}
\cnode*(3,1){4pt}{A}
\cnode*(3,-1){4pt}{C}
\psset{nodesep=3pt,shortput=tablr}
\ncline{root}{A}^{$x$}
\ncline{root}{C}_{$y$}
\ncline{A}{C}>{$z$}
\end{document}