module main {
  type state_t = enum { RED, GREEN }; // Define state types as RED and GREEN

  var light_state : state_t; // Variable to hold the current state of the traffic light

  // Initial state of the traffic light is set to RED
  init {
    light_state = RED;
  }

  // Transition system to toggle between RED and GREEN
  next {
    if (light_state == RED) {
      light_state' = GREEN;
    } else {
      light_state' = RED;
    }
  }

  // Specification to check if the light eventually turns GREEN from RED
  // and vice versa
  invariant always_red_or_green : (light_state == RED) || (light_state == GREEN);

  // Control block to run the model
  control {
    // Unrolling the transition system for multiple steps to simulate the traffic light behavior
    v = unroll(10);
    check;
    print_results;
  }
}
