\begin{frame}
  \frametitle{Examples}

  \begin{exampleblock}{$\myall{x}{A(x)} \;\vdash\;  A(c) \wedge A(d)$}
  \begin{tikzpicture}
    \naturaldeduction{
      \proofstep{$\myall{x}{A(x)}$}{premise};
    \proofstep{$A(c)$}{$\forall e\;$ 1};
    \proofstep{$A(d)$}{$\forall e\;$ 1};
        \proofstep{$A(c) \wedge A(d)$}{$\wedge i\;$ 2,\; 3};
    }
  \end{tikzpicture}
  \end{exampleblock}
\end{frame}