%% 
%%  The LaTeX Graphics Companion, 2ed (first printing May 2007)
%% 
%%  Example 7-4-42 on page 507.
%% 
%%  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}
\[
\renewcommand{\labelstyle}{\scriptstyle}
\renewcommand{\objectstyle}{\scriptstyle}
\knotholesize{3mm}
\renewcommand\Vcap[2]{\save 0;#2-#1:#1,
  \vcap~{#1+(0,1)}{#2+(0,1)}{#1}{#2}\restore}
\xygraph{!{0;/r5mm/:}
  !P3"t"{~>{.}~*{\xypolynode}}
  !P6"h"{~:{(4.5,0):}~>{.}~*{\xypolynode}}
  !{\xunderv~{"h2"}{"h1"}{"t1"}{"t3"}@(.62)}
  !{\xunderv~{"h4"}{"h3"}{"t2"}{"t1"}@(.62)}
  !{\xunderv~{"h6"}{"h5"}{"t3"}{"t2"}@(.62)}
  !{\Vcap{"h3"}{"h2"}\Vcap{"h5"}{"h4"}%
    \Vcap{"h1"}{"h6"}}
}\]
\end{document}