$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.89
\begin{equation} \begin{gathered}\label{equation:anchor-easy} \xymatrix { \operatorname{\mathcal{E}}' \ar [r]^{\iota '} \ar [d]^{U} & \overline{\operatorname{\mathcal{E}}}' \ar [d]^{\overline{U}} \\ \operatorname{\mathcal{E}}\ar [r]^{\iota } \ar [d] & \overline{\operatorname{\mathcal{E}}} \ar [d] \\ \operatorname{\mathcal{C}}\ar [r] & \operatorname{\mathcal{C}}^{\triangleright } } \end{gathered} \end{equation}