\documentclass{book}
\usepackage{pstricks,pst-node,amssymb,amsmath,graphics,latexsym,tabularx,shapepar}
\usepackage[all,cmtip,2cell,line]{xypic}
\UseAllTwocells\SilentMatrices
\begin{document}
$$\xymatrix{
 P^{\prime}
\ar@/_/[ddr]_{p_{2}^{\prime}} \ar@/^/[ddr]^{p_{1}^{\prime}}\ar@[dr]_{p}
\\
& P \ar[d]^{p_{2}}\ar[r]_{p_{1}}&X_{1}\ar[d]_{f_{1}}
\\
&X_{2}\ar[r]^{f_{2}}&Y }$$
\end{document}