$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
5.61
\begin{equation} \begin{gathered}\label{equation:pullback-cocartesian-fibration} \xymatrix@R =50pt@C=50pt{ \operatorname{\mathcal{E}}\ar [r]^-{F} \ar [d]^{U'} & \operatorname{\mathcal{E}}\ar [d]^{U} \\ \operatorname{\mathcal{C}}' \ar [r]^-{\overline{F}} & \operatorname{\mathcal{C}}, } \end{gathered} \end{equation}