\documentclass{ppex}
\nonstopmode
\usepackage [curve,knot,graph,dvips]{xy}
\pagestyle{empty}
\setlength\textwidth{183.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage [curve,knot,graph,dvips]{xy}
\[\xygraph{!{0;/r10mm/:}
         !{\vover}
     [u] !{\hcap[-2]}
     [d] !{\vover-}
   [ruu] !{\hcap[2]}
}\]
\[\begin{xy} 0;/r10mm/:
  ,\hcap[-2]\vunder\vunder-
  ,+(1,2),\hcap[2]
\end{xy}\]
\end{document}
