\begin{frame}
  \frametitle{Example}

  \begin{exampleblock}{}
  Prove \quad$p \vee \neg q,\; \neg p \to q \;\vdash\; p$\quad!
  \medskip

  \begin{tikzpicture}
  \naturaldeduction{
    \mpause[1]{
      \proofstep{$p \vee \neg q$}{premise};
    }
    \mpause{
      \proofstep{$\neg p \to q$}{premise};
    }
    \mpause{
      \proofbox{
        \mpause{
          \proofstep{$p$}{assumption};
        }
      }
    }
    \mpause{
      \proofbox{
        \mpause{
          \proofstep{$\neg q$}{assumption};
        }
        \mpause{
          \proofstep{$\neg\neg p$}{MT 2,4};
        }
        \mpause{
          \proofstep{$p$}{$\neg\neg_e$ 5};
        }
      }
    }
    \mpause{
      \proofstep{$p$}{$\vee_e$ 1,\;3--3,\;4--6};
    }
  }
  \end{tikzpicture}
  \end{exampleblock}
\end{frame}