$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.64
\begin{equation} \begin{gathered}\label{equation:relative-diagonal} \xymatrix { Y \times _{X} Y \ar [r]^{ \pi } \ar [d]^{\pi '} & Y \ar [d]^{f} \\ Y \ar [r]^{f} & X } \end{gathered} \end{equation}