$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
5.59
\begin{equation} \begin{gathered}\label{equation:isomorphism-extension-small-diagram} \xymatrix@R =50pt@C=50pt{ \operatorname{\mathcal{E}}_0 \ar [r]^-{G_0} \ar [d]^{U_0} & \operatorname{\mathcal{E}}' \ar [d]^{V} \\ \operatorname{\mathcal{C}}_0 \ar [r] & \operatorname{\mathcal{C}}} \end{gathered} \end{equation}