$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.55
\begin{equation} \begin{gathered}\label{equation:hard-half-of-detection} \xymatrix@R =50pt@C=50pt{ \operatorname{\mathcal{E}}' \ar [d]^{U'} \ar [r] \ar [d] & \overline{\operatorname{\mathcal{E}}}' \ar [d]^{ \overline{U}' } \\ \operatorname{\mathcal{C}}' \ar [r] & \operatorname{\mathcal{C}}'^{\triangleright }, } \end{gathered} \end{equation}