Kerodon

$\Newextarrow{\xRightarrow}{5,5}{0x21D2}$ $\newcommand\empty{}$
$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
9.10
\begin{equation} \begin{gathered}\label{equation:lifting-problem-in-homotopy2} \xymatrix@R =50pt@C=50pt{ A \ar [d]^{[f]} \ar [r]^-{[u_0]} & X \ar [d]^{[g]} \\ B \ar [r]^-{ [\overline{u}] } \ar@ {-->}[ur] & Y. } \end{gathered} \end{equation}