$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
6.2
\begin{equation} \begin{gathered}\label{equation:S-optimal} \xymatrix@R =50pt@C=50pt{ & Y \ar [dr]^{s} & \\ X \ar [ur]^{g} \ar [rr]^{f} & & Z } \end{gathered} \end{equation}