\documentclass{ppex}
\nonstopmode
\usepackage {xy}
\pagestyle{empty}
\setlength\textwidth{207.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {xy}
\[\begin{xy}
  0*{DL} ,+/r1cm/*{DR}
 ,<0cm,1cm>*{UL} ,<1cm,1cm>*{UR}
 ,(5,5)*{5,5}
\end{xy}\]
\end{document}