$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
3.81
\begin{equation} \label{equation:unit-of-realization-1} \begin{gathered} \xymatrix@R =50pt@C=50pt{ \operatorname{\partial \Delta }^{n} \ar [r] \ar [d] & \Delta ^ n \ar [d] \\ X' \ar [r] & X, }\end{gathered} \end{equation}