$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.71
\begin{equation} \begin{gathered}\label{equation:bad-equalizer} \xymatrix@C =50pt@R=50pt{ \{ x\} \times ^{\mathrm{h}}_{X} \{ y\} \ar [r]^-{f} & \Delta ^0 \ar@ <.4ex>[r]^-{x} \ar@ <-.4ex>[r]_-{y} & X } \end{gathered} \end{equation}