\begin{frame}
  \frametitle{Parse Trees}

  \begin{exampleblock}{
  We make a parse tree from the formula
  $$\myex{y}{ \myall{z}{ (\myex{x}{R(x,z)} \to (R(x,z) \wedge R(y,z))) }}$$
  }
  \pause
  \begin{center}
  \tikz[level distance=9mm,
    level 1/.style={sibling distance=20mm},
    level 2/.style={sibling distance=35mm},
    level 3/.style={sibling distance=30mm},
    level 4/.style={sibling distance=17mm},
    level 5/.style={sibling distance=8mm},
    ]
  \node {$\exists y$}
    child {node {$\forall z$}
      child {node   {$\to$}
        child {node {$\exists x$}
         child {node {$R$}
           child {node {$x$} }
           child {node {$z$} }
         }
        }
        child {node  {$\wedge$}
         child {node {$R$}
           child {node {$x$} }
           child {node {$z$} }
         }
         child {node {$R$}
           child {node {$y$} }
           child {node {$z$} }
         }
        }
      }
    };
  \end{center}
  \end{exampleblock}
  \pause
  
  \begin{alertblock}{}
    The $x$ on the left is in the scope of $\exists x$; the $x$ in the middle not.
  \end{alertblock}
\end{frame}