\documentclass[a4paper,11pt]{amsart}
\usepackage{mathtext}
\usepackage{amssymb}
\usepackage[all]{xy}
\usepackage[T2A]{fontenc}
\usepackage[cp1251]{inputenc}
\usepackage[russian]{babel}
\begin{document}
$$\begin{xy}/r1cm/:;
(0,0)*+{\bullet};(0.6,0.8)*+{\bullet};(-0.6,0.8)*+{\bullet};(0,1)*+{\bullet};
(0,0)*\xycircle(1,1){-};(0,0)*\xycircle(0.15,0.15){-};
(-0.6,0.8);(-0.2,1.1)**@{-}*@{>}*+!RD{\bar p};
(0.6,0.8);(0.2,1.1)**@{-}*@{>}*+!LD{\bar p};
(0,1);(0,0.4)**@{-}*@{>}*+!LL{m\bar g}\end{xy}$$
\end{document}