Kerodon

\begin{equation} \begin{gathered}\label{equation:base-change-relative-limit} \xymatrix@R =50pt@C=50pt{ \operatorname{\mathcal{D}}' \ar [rr]^{H'} \ar [dr] \ar [dd]^{G} & & \operatorname{\mathcal{E}}' \ar [dl] \ar [dd] \\ & \operatorname{\mathcal{B}}' \ar [dd] & \\ \operatorname{\mathcal{D}}\ar [dr]_{ U } \ar [rr]^(.4){H} & & \operatorname{\mathcal{E}}\ar [dl]^{V} \\ & \operatorname{\mathcal{B}}& } \end{gathered} \end{equation}