$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
3.43
\begin{equation} \begin{gathered}\label{equation:composite-homotopy-pullback} \xymatrix@R =50pt@C=50pt{ Z \ar [r] \ar [d]^{h} & Y \ar [r] \ar [d]^{g} & X \ar [d]^{f} \\ U \ar [r] & T \ar [r] & S } \end{gathered} \end{equation}