\begin{frame}{Example: $\unpred{P}{c},\, \neg \unpred{P}{d} \;\vdash\; \neg \;c=d$}
  \begin{exampleblock}{}
    \begin{tikzpicture}
      \naturaldeduction{
        \proofstep{$\unpred{P}{c}$}{premise};   
        \proofstep{$\neg \unpred{P}{d}$}{premise}; 
        \mpause[1]{     
        \proofbox{
          \proofstep{$c=d$}{assumption};
          \mpause{ \proofstep{$\unpred{P}{d}$}{$=_e\;$ 3,1}; }
          \mpause{ \proofstep{$\bot$}{$\neg_e\;$ 2,4} }
        }
        \mpause{ \proofstep{$\neg\; c=d$}{$\neg_i\;$ 3--5}; }
        }
      }
    \end{tikzpicture}
  \end{exampleblock}
\end{frame}