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

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

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

    // Define the transition relation for the traffic light
    next {
        // Transition from RED to GREEN and from GREEN to RED
        if (current_state == RED) {
            current_state' = GREEN;
        } else {
            current_state' = RED;
        }
    }

    // Define properties to check
    // For instance, check that the traffic light does not remain in the same state
    invariant no_skip_states : (current_state == RED && current_state' == GREEN) || (current_state == GREEN && current_state' == RED);
}

// Main module to run and control the model
module main {
    // Instance of the traffic light module
    instance tl : traffic_light;

    // Control block for model checking
    control {
        // Run bounded model checking for a few steps to see the transitions
        v = unroll(5);
        check;
        print_results;
    }
}
