module traffic_light {
  // Define the states of the traffic light
  type light_state_t = enum { RED, GREEN };

  // Variable to hold the current state of the traffic light
  var current_state : light_state_t;

  // Initialize the traffic light state to RED
  init {
    current_state = RED;
  }

  // Define the transition between states
  next {
    current_state' = match (current_state) {
      RED   : GREEN;
      GREEN : RED;
    };
  }

  // Safety property: The traffic light cannot be red and green at the same time
  invariant is_valid_state : (current_state == RED) || (current_state == GREEN);

  // Control block for bounded model checking
  control {
    v = unroll(5); // Check the behavior for 5 transitions
    check;
    print_results;
  }
}
