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\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}