Kerodon

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9.6
\begin{equation} \begin{gathered}\label{equation:lifting-problem-ordinary} \xymatrix@R =50pt@C=50pt{ A \ar [d]^{f} \ar [r]^-{u_0} & X \ar [d]^{g} \\ B \ar [r]^-{\overline{u}} & Y } \end{gathered} \end{equation}