$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
8.75
\begin{equation} \begin{gathered}\label{equation:check-second-condition} \xymatrix@C =50pt@R=50pt{ \overline{X} \ar [d]^{\operatorname{id}} & \overline{X} \ar [l]_{\operatorname{id}} \ar [d]^{u} & \overline{Y} \ar [l]_{e} \ar [d]^{v} \\ \overline{X} \ar [r]^-{u} & \overline{X}' \ar [r] & \overline{Y}'. } \end{gathered} \end{equation}