$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
4.17
\begin{equation} \begin{gathered}\label{equation:pullback-of-core} \xymatrix@R =50pt@C=50pt{ \operatorname{\mathcal{C}}'^{\simeq } \ar [r] \ar [d]^{q'^{\simeq }} & \operatorname{\mathcal{C}}^{\simeq } \ar [d]^{q^{\simeq }} \\ \operatorname{\mathcal{D}}'^{\simeq } \ar [r] & \operatorname{\mathcal{D}}^{\simeq } } \end{gathered} \end{equation}