%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 7-4-43 on page 508.
%% 
%%  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[all,knot,poly,dvips]{xy}
\StopShownPreambleCommands
\begin{document}
\renewcommand{\labelstyle}{\scriptstyle}
\renewcommand{\objectstyle}{\scriptstyle}
\[\xygraph{!{0;/r2mm/:}
  !P3"t"{~>{.}}
  !P6"h"{~:{(4.5,0):}~>{.}~*{\xypolynode}}
  !P12"d"{~:{(9,0):}~>{.}~*{\xypolynode}}
  !P12"D"{~:{(13.,0):}~>{.}~*{\xypolynode}}
  !{\xoverv~{"h2"}{"h1"}{"t1"}{"t3"}@(.62)}
  !{\xoverv~{"h4"}{"h3"}{"t2"}{"t1"}@(.62)}
  !{\xoverv~{"h6"}{"h5"}{"t3"}{"t2"}@(.62)}
  !{\vover~{"d4"}{"d3"}{"h3"}{"h2"}}
              ,"d4"-@`{"D5","D6"}"d7",
  !{\vover~{"d8"}{"d7"}{"h5"}{"h4"}}
              ,"d8"-@`{"D9","D10"}"d11",
  !{\vover~{"d12"}{"d11"}{"h1"}{"h6"}}
              ,"d12"-@`{"D1","D2"}"d3"
}\]
\end{document}