
module main {
    // Variables definition
    var coin : integer;
    var dispensed_drinks : integer;

    // Initialization
    init {
        coin = 0;
        dispensed_drinks = 0;
    }

    // Transition relation
    next(coin) := 
        case
            coin <= 10 : coin + 1; // Up to a limit for illustration
            true : coin;
        esac;

    next(dispensed_drinks) := 
        case
            coin > dispensed_drinks : dispensed_drinks + 1;  // Dispense drink only if there are enough coins
            true : dispensed_drinks;
        esac;

    // Safety property
    // Ensure the number of inserted coins is always at least the number of dispensed drinks
    invariant safety_property {
        coin >= dispensed_drinks
    }
}