%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 6-2-40 on page 352.
%% 
%%  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[radius=0.3cm](0.25,0){A}%
\Cnode[radius=0.3cm](2.5,0){B}
\ncbar[angle=90]{->}{A}{B}%
\ncbar[angle=-90,arm=0.2cm]{->}{B}{A} \\[10mm]
\Cnode[radius=0.3cm](0.25,0){A}%
\Cnode[radius=0.3cm](2.5,0){B}
\psset{linearc=0.2cm}
\ncdiag[angle=90]{->}{A}{B}%
\ncdiag[angle=-90,armA=0.2cm,armB=0.75cm]{->}{B}{A}
\end{document}