%======================= main.tex ===========================================
\documentstyle{slides}
%\input{mssymb}
%\newtheorem{exam}{Example}[section]
%\newtheorem{prop}{Proposition}[section]  
%\newtheorem{lem}{Lemma}[section]  
%\newtheorem{thm}{Theorem}[section]  
%\newtheorem{cor}{Corollary}[section]  
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\begin{document}
test
\blackandwhite{example}
\end{document}