$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
3.53
\begin{equation} \label{equation:mather-first-cube1} \begin{gathered} \xymatrix@R =50pt@C=50pt{\overline{A} \ar [rr] \ar [dd] \ar [dr] & & \overline{B} \ar [dd] \ar [dr] & \\ & \overline{C} \ar [rr] \ar [dd] & & \overline{D} \ar [dd] \\ A \ar [rr] \ar [dr] & & B \ar [dr] & \\ & C \ar [rr] & & D } \end{gathered}\end{equation}