$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
8.59
\begin{equation} \begin{gathered}\label{equation:E-plusminus-covariant-transport} \xymatrix@R =50pt@C=50pt{ \operatorname{\mathcal{E}}_{-} \ar [d]^{ U_{-} } \ar [r] & \operatorname{Tw}(\operatorname{\mathcal{C}}_{-} ) \ar [d] \\ \operatorname{\mathcal{C}}_{-}^{\operatorname{op}} \times ( \operatorname{\mathcal{C}}_{-} \vec{\times }_{\operatorname{\mathcal{C}}} \operatorname{\mathcal{C}}) \ar [r] & \operatorname{\mathcal{C}}_{-}^{\operatorname{op}} \times \operatorname{\mathcal{C}}_{-}. } \end{gathered} \end{equation}