node reach_verif(day_event,night_event,noon_event:bool) = (day_state,evening_state:bool)

  contract
  reachable evening_state

let
    automaton
    state Night do day_state = false; evening_state = false
    until day_event then Day
    state Day do
      day_state = true;
      automaton
      state Morning do
        evening_state = false;
      until noon_event then Afternoon
      state Afternoon do
        evening_state = false;
      until night_event then Evening
      state Evening do
        evening_state = true;
      until day_event then Morning
      end
    until night_event then Night
    end
tel