\documentclass{ppex}
\nonstopmode
\usepackage [all,2cell]{xy}
\pagestyle{empty}
\setlength\textwidth{183.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage [all,2cell]{xy}
\UseTwocells
\[
\xymatrix @R=2.0pc @C=.8pc {
& \bullet \ar @/^1ex/ [rr]
&& \bullet \ar @/^1ex/ [dr]
\\ \bullet \urtwocell<2> \rrtwocell<2>
           \drtwocell<2> \xtwocell[1,3]{}\omit
           \xtwocell[-1,3]{}\omit
&& \bullet \ar @/_1ex/ [ur]
           \ar @/^1ex/ [dr]
           \rrtwocell\omit
&& \bullet
\\ & \bullet \ar @/_1ex/ [rr]
&&   \bullet \ar @/_1ex/ [ur]
}\]
\end{document}