\documentclass{ppex}
\nonstopmode
\usepackage [all,poly,knot,dvips]{xy}
\pagestyle{empty}
\setlength\textwidth{183.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage [all,poly,knot,dvips]{xy}
\[\UseTips
\renewcommand{\labelstyle}{\scriptstyle}
\begin{xy} 0;/r8mm/:
  (0,0)
 ,{\hover\hcross<><{1}|>|{2}>>>{3}%
    \hcross<><{4}|>|{5}>>>{6}\hover-}
 ,(0,-3)
 ,{\hover\htwistneg<><{1}|>|{2}>>>{3}%
   \htwistneg<><{4}|>|{5}>>>{6}\hover-}
\end{xy}\]
\end{document}