%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%% %1 %%%%%%%%%%%%%%%%%%%%%%%%% \chapter{Prove that if $A = B$, then $A \subseteq B$ and $B \subseteq A$.} \label{pf:1} \section{First draft} Due Monday, February 8 at 6:00 PM. \begin{proof} Write your proof here. \end{proof} \section{Second draft} \begin{proof} After receiving my comments, write your revised proof here. (Do not make changes in the first section.) \end{proof}