% \begin{frame}{Looking Back}
%   \structure{Last Lecture:}
%   \medskip
% 
%   \begin{goal}{}
%   The following statements are equivalent:
%   \medskip
%   \begin{itemize}\setlength{\itemsep}{2ex}
%   \item There is a \alert{DFA} $M$ with $L(M) = L$.
%   \item There is an \alert{NFA} $M$ with $L(M) = L$.
%   \item There is a \alert{right linear grammar} $G$ with $L(G) = L$.
%   \item There is a \alert{left linear grammar} $G$ with $L(G) = L$.
%   \item There is a \alert{regular expression} $r$ with $L(r) = L$.
%   \end{itemize}
%   \medskip
%   \end{goal}
% \end{frame}

\subsection{Elementary Properties of Regular Languages}

\themex{Elementary Properties of Regular Languages}