\documentclass{article}
\usepackage{amsthm}
\input{flavor}

\newtheorem{theorem}{Theorem}

\begin{document}

\begin{theorem}
  $(a+b)^2=a^2 + 2ab + b^2$
\end{theorem}
\begin{proof}
  $(a+b)^2=(a+b)(a+b)=a(a+b)+b(a+b)= a^2+ab+ba+b^2=a^2+ab+ab+b^2=a^2+2ab+b^2$
\end{proof}

\end{document}
