\documentclass{ppex}
\nonstopmode
\usepackage {xy}
\pagestyle{empty}
\setlength\textwidth{183.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {xy}
\[\begin{xy}
 0*=+{l}="l" ;<2cm,8mm>*=+{r}="r" **@{-}
,<4mm,10mm>*+{ll} ;<25mm,2mm>*+{rr} **@{--}
?!{"r";"l"}*{\oplus}
\end{xy}\]
\end{document}

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