\begin{frame}{Exercise}
  \bigskip
  
%   (In groups of two, 3 minutes)
  \begin{exampleblock}{}
    Let
    \begin{itemize}
      \item $\Sigma = \{\,a,b\,\}$
      \item $L = \{\,ab^n \mid n \geq 0 \,\}$
    \end{itemize}
    \medskip
    
    Describe the following languages as sets:
    \begin{align*}
      L^R  &= \mpause[1]{ \{\, b^na \mid n \ge 0\,\}} \\
      \mpause{\overline{L}  &=} \mpause{\{\,\lambda\,\}} \mpause{\cup \{\, bw \mid w\in \Sigma^* \,\}} \mpause{\cup \{\, awau \mid w,u\in \Sigma^* \,\}} 
    \end{align*}
  \end{exampleblock}
  \pause\pause\pause\pause\pause\pause\bigskip
  
  \begin{alertblock}{}
    Set notation is not ideal to describe languages.
  \end{alertblock}
\end{frame}