\begin{frame}{Ambiguous Grammars}
  
  \begin{exampleblock}{}
    Is the following grammar ambiguous?
    \begin{talign}
      S \to S+0 \mid 0
    \end{talign}
    \pause
    No, every word has precisely one derivation tree.
  \end{exampleblock}
  \pause\bigskip
  
  \begin{exampleblock}{}
    Note that both grammars
    \begin{talign}
      S \to S+S \mid 0 &&
      S \to S+0 \mid 0
    \end{talign}
    generate the same language:
    \begin{talign}
      \{\, 0(+0)^n \mid n \geq 0 \,\}
    \end{talign}
  \end{exampleblock}
\end{frame}