$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
11.6
\begin{equation} \label{diagram:categorical-pushout-square2} \begin{gathered} \xymatrix@R =50pt@C=50pt{ A \ar [r]^-{f} \ar [d] & B \ar [d] \\ C \ar [r] & D. } \end{gathered} \end{equation}