$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
8.64
\begin{equation} \begin{gathered}\label{equation:retraction-diagram-primordial} \xymatrix@R =50pt@C=50pt{ & X \ar [dr]^{ r } & \\ Y \ar [ur]^{i} \ar [rr]^{ \operatorname{id}_ Y } & & Y. } \end{gathered} \end{equation}