\begin{frame}
  \frametitle{Example}

  \begin{exampleblock}{}
  Use $\bot_e$ to prove \quad$\neg p \vee q \;\vdash\; p \to q$\quad!
  \medskip

  \begin{tikzpicture}
  \naturaldeduction{
    \mpause[1]{
      \proofstep{$\neg p \vee q$}{premise};
    }
    \mpause{
      \proofbox{
        \mpause{
          \proofstep{$p$}{assumption};
        }
        \mpause{
          \proofbox{
            \mpause{
              \proofstep{$\neg p$}{assumption};
            }
            \mpause{
              \proofstep{$\bot$}{$\neg_e$ 2,3};
            }
            \mpause{
              \proofstep{$q$}{$\bot_e$ 4};
            }
          }
        }
        \mpause{
          \proofbox{
            \mpause{
              \proofstep{$q$}{assumption};
            }
          }
        }
        \mpause{
          \proofstep{$q$}{$\vee_e$ 1,\;3--5,\;6--6};
        }
      }
    }
    \mpause{
      \proofstep{$p\to q$}{$\to_i$ 2--7};
    }
  }
  \end{tikzpicture}
  \end{exampleblock}
\end{frame}