\begin{frame}
  \frametitle{Exam Preparation Exercises}

  \begin{example}{}
  \begin{center}
    \begin{tikzpicture}[
        default,
        point/.style={circle, draw=blue, thick, inner sep=3pt, minimum size=7mm},
        node distance=20mm]
  
      \foreach \n in {0,1,...,7} {
        \node (\n) at (\n*360/8:2cm) [point] {};
      }

      \foreach \n in {0,1,7} {
        \node [ro=\n] {$w_\n$};
      }
      \foreach \n in {3,4,5} {
        \node [lo=\n] {$w_\n$};
      }
      \node [ao=2] {$w_2$};
      \node [bo=6] {$w_6$};
      
      \begin{scope}[shorten <= 1mm, shorten >= 1mm, very thick,>=stealth]
      \foreach \n/\m in {0/1,1/2,2/3,3/4,4/5,5/6,6/7,7/0} {
        \draw [->] (\n) to[bend left=15] (\m);
        \draw [->] (\m) to[bend left=15] (\n);
      }
      
      \node at (1) {$\lab{p}$};
      \node at (3) {$\lab{p}$};
      \end{scope}
    \end{tikzpicture}
    \vspace{1ex}
  \end{center}
  
  Determine in which worlds the following formula holds:
  \begin{talign}
    &\some\some\some\some\all p  & \mbox{\DARKRED{?}}
  \end{talign}
  \end{example}
\end{frame}