\begin{frame}{Example}
  
  \begin{exampleblock}{}
    Consider the following NPDA with stack starting symbol $z=0$:
    \begin{center}
      \vspace{-1ex}
      \begin{tikzpicture}[default,node distance=25mm,->,s/.style={minimum size=5mm}]
        \node (q0) [state,s] {$q_0$}; \draw ($(q0) + (-8mm,0mm)$) -- (q0); 
        \node (q1) [fstate,s,right of=q0] {$q_1$};
    
        \draw (q0) to[bend left=20] node [label,above,align=center] {$a[0/10]$\\$c[1/11]$} (q1);
        \draw (q1) to[bend left=20] node [label,below] {$c[1/1]$} (q0);
        \draw (q1) to[tloop] node [label,above] {$b[1/\lambda]$} (q1);
      \end{tikzpicture}
      \vspace{-2ex}
    \end{center}
    Ensure that the final state is only be reached with empty stack.
  \end{exampleblock}
  \pause
  
  \begin{goal}{}
    We already know how to transform acceptance with final states to acceptance with empty stack.
    \pause
    \emph{Here no fresh start state is needed;} the symbol $0$ always remains at the bottom.
  \end{goal}
  \pause
  
  \begin{exampleblock}{}
    \begin{center}
      \input{tikz/npda4.tex}
    \end{center}
  \end{exampleblock}
\end{frame}