$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
8.56
\begin{equation} \begin{gathered}\label{diagram:Hom-witness} \xymatrix@R =50pt@C=50pt{ \operatorname{Tw}(\operatorname{\mathcal{C}}) \ar [r] \ar [d] & \{ \Delta ^0 \} \operatorname{\vec{\times }}_{\operatorname{\mathcal{S}}} \operatorname{\mathcal{S}}\ar [d] \\ \operatorname{\mathcal{C}}^{\operatorname{op}} \times \operatorname{\mathcal{C}}\ar [r]^-{ \mathscr {H} } & \operatorname{\mathcal{S}}. } \end{gathered} \end{equation}