\begin{frame}[fragile]
  \frametitle{Examples}
  
  \begin{exampleblock}{Example: $(p \to q) \to r \;\;\vdash\;\; p \to (q \to r)$}
  \medskip{\small
  \begin{verbatim}
Theorem ex3 : ((A -> B) -> C) -> (A -> (B -> C)).\end{verbatim}
  \pause
  \begin{verbatim}
  Proof.
  imp_i H.
  imp_i HA.
  imp_i HB.
  imp_e (A -> B).
  ass H.
  imp_i HA'.
  ass HB.
  Qed.\end{verbatim}
  \smallskip}
  \end{exampleblock}  
\end{frame}