$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
9.23
\begin{equation} \begin{gathered}\label{equation:discrete-via-slicing} \xymatrix { \operatorname{\mathcal{C}}_{/X} \ar [r] \ar [d] & \mathrm{h}_{\mathit{\leq n}}\mathit{(\operatorname{\mathcal{C}})}_{/X} \ar [d] \\ \operatorname{\mathcal{C}}\ar [r] & \mathrm{h}_{\mathit{\leq n}}\mathit{(\operatorname{\mathcal{C}})} } \end{gathered} \end{equation}