\item \self
    Consider an ordinary traffic junction with incoming lanes from the north, south, east and west. We want to formulate relevant constraints that a traffic light system has to fulfill.

    Give a set of propositional variables that model whether the north and south \emph{or} the east and the west get the
    \begin{itemize}
      \itemsep0em
      \item green,
      \item yellow or
      \item red
    \end{itemize}
    light, respectively. \\

    Formulate the following sentences using \emph{$CTL^\star$}:
    \begin{enumerate}[label=(\alph*)]
      \item The north/south lanes will never get the green light at same time as the east/west lanes.
      \item Whenever the north/south lane receive the green light it will stay green until it changes to yellow.
      \item When the east/west lane has the red light, it will eventually get the yellow and red light until the light switches to green.
    \end{enumerate}
