\documentclass{ppex}
\nonstopmode
\usepackage [all,arc,dvips]{xy}
\pagestyle{empty}
\setlength\textwidth{231.0pt}
\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage [all,arc,dvips]{xy}
\[\begin{xy} 0;/r20mm/:
  (0,0)="o" ,*@{*} ,*+!U{o}
 ,(-1.0,0.5)="p"*@{o},*+!LD{p_1}
 ,{\ar @{-->} "o";"p"};
 (-2.,0.)="c",*@{*},*+!L{c_1}
 ,"c",{\ellipse_{}},{\ellipse^{.}}
 ,(1.8,0.4)="p",*@{o},*+!D{p_2}
 ,{\ar @{-->} "o";"p"};
 (0.8,-1)="c",*@{*},*+!R{c_2}
 ,"c",{\ellipse{}}
\end{xy}\]
\end{document}

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