\documentclass[a4paper,12pt]{article}
\usepackage{amsthm,amssymb,amsmath}
\usepackage[all]{xy}
\usepackage{xepersian}
\begin{document}
\begin{displaymath}
\xymatrix{ & \bullet \ar[dl]_d \ar[dr]^u & \\
\bullet \ar[dr] & & \bullet \ar[dl] \\
& \bullet }
\end{displaymath}
\end{document}