$\Newextarrow{\xhookrightarrow}{10,10}{0x21AA}$
7.66
\begin{equation} \begin{gathered}\label{equation:equalizer-not-in-homotopy} \xymatrix@C =50pt@R=50pt{ Z \ar [r]^-{g} & Y \ar@ <.4ex>[r]^-{f_0} \ar@ <-.4ex>[r]_-{f_1} & X } \end{gathered} \end{equation}