$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
6.10
\begin{equation} \begin{gathered}\label{equation:short-morphisms} \xymatrix { L_{t} \ar [r] \ar [d] & \operatorname{\mathcal{C}}^{\leq p}_{< t}(n) \ar [d] \\ \Delta ^{n+1} \ar [r]^{ \sigma _{t}^{+} } & \operatorname{\mathcal{C}}^{\leq p}_{\leq t}(n). } \end{gathered} \end{equation}