$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.21
\begin{equation} \begin{gathered}\label{equation:relative-Kan-extension-existence3} \xymatrix@R =50pt@C=50pt{ \operatorname{\mathcal{K}}_{C} \ar [r] \ar [d] & \operatorname{\mathcal{D}}\ar [d]^{U} \\ \operatorname{\mathcal{K}}_{C} \star _{ \{ C \} } \{ C\} \ar@ {-->}[ur]^{ \overline{F}_ C } \ar [r] & \operatorname{\mathcal{E}}. } \end{gathered} \end{equation}