\begin{frame}
  \frametitle{Undecidable Properties of Context-Free Languages}

  \begin{goal}{}
    Undecidable properties of context-free languages:
    \begin{itemize}
      \item empty intersection
      \item ambiguity
      \item palindromes
      \item equality
      \item \ldots
    \end{itemize}
    \medskip
  \end{goal}  
\end{frame}