$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
5.27
\begin{equation} \begin{gathered}\label{equation:comparison-map-over-edge} \xymatrix@R =50pt@C=50pt{ \emptyset \star _{X} X \ar [r] \ar [d] & \emptyset \star _{Y} Y \ar [d] \\ X \star _{X} X \ar [r] & X \star _{Y} Y. } \end{gathered} \end{equation}