%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 6-1-41 on page 332.
%% 
%%  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{135.83385pt}
\StartShownPreambleCommands
\usepackage{pstricks,pst-plot}
\StopShownPreambleCommands
\begin{document}
\psset{unit=2.0}
\newcommand\PSfunction[1]{t t mul 1 sub #1 mul t t mul 1 add div
  t t mul 1 sub t mul #1 mul t t mul 1 add div}
\begin{pspicture}(-1.1,-1.1)(1.1,1.1)
  \psgrid[subgriddiv=0,griddots=10,gridlabels=7pt]
  \psset{plotpoints=200,linewidth=1.5pt}
  \parametricplot{-1.85}{1.85}{\PSfunction{1}}
  \psset{linestyle=dashed}
  \parametricplot{-4.5}{4.5}{\PSfunction{0.25}}
  \parametricplot{-2.1}{2.1}{\PSfunction{0.75}}
  \rput[r](-0.05,-0.5){$a=1;\ 0.75;\ 0.25$}
\end{pspicture}
\end{document}