$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.48
\begin{equation} \begin{gathered}\label{equation:witness-vs-section} \xymatrix { S \ar [r] \ar [d] & S_0 \ar [d] \\ S_1 \ar [r] & S_{01} } \end{gathered} \end{equation}