$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
11.17
\begin{equation} \begin{gathered}\label{equation:mapping-space-homotopy-pullback} \xymatrix@R =50pt@C=50pt{ \operatorname{Fun}_{/S}(A', Y) & \operatorname{Fun}_{/S}(A, Y) \ar [l] \\ \operatorname{Fun}_{/S}(B',Y) \ar [u] & \operatorname{Fun}_{/S}(B, Y) \ar [u] \ar [l] } \end{gathered} \end{equation}