%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 7-3-2 on page 476.
%% 
%%  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{183.83385pt}
\StartShownPreambleCommands
\usepackage[curve]{xy}
\StopShownPreambleCommands
\begin{document}
\[\begin{xy}
  0*+{L};(50,20)*+{R}
  **\crv{~*=<2mm>{.}(20,30)&(30,35)}
  **\crv~Lc{~**@{==}~*{\bullet}%
       (20,-15)&(30,-15)}
\end{xy}\]

\end{document}