$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.87
\begin{equation} \begin{gathered}\label{equation:infinitary-disjoint-coproducts} \xymatrix { \emptyset \ar [r] \ar [d] & X_ i \ar [d]^{f_ i} \\ X_ j \ar [r]^{ f_ j } & X } \end{gathered} \end{equation}