// Define modules for ArrivalDetector and DepartureDetector
module ArrivalDetector {
    output arrival : boolean;
    // Logic to set arrival=true when a car arrives would go here
}

module DepartureDetector {
    output departure : boolean;
    // Logic to set departure=true when a car departs would go here
}

// Define the Counter module
module Counter {
    input arrival_event : boolean;
    input departure_event : boolean;
    var counter : int;

    init {
        counter = 0; // Initialize counter
    }

    next {
        if (arrival_event) {
            counter = counter + 1;
        } else if (departure_event) {
            counter = counter - 1;
        }
    }
}

// Define the main module to orchestrate the interactions
module main {
    // Instance creation and connections would be defined here
    // Logic to simulate arrivals and departures and update the counter
}
