GlobalObject.swift

class GlobalObject {
    func cleanVehicle()
}

class Vehicle: GlobalObject {
    func refuel()
}

class Car: Vehicle {
    func drive()
}

class CleanerCar: Car {}

class Motorbike: Vehicle {
    func ride()
}

class Robot: GlobalObject {
    func findVehicle()
}

class Mechanic: Robot {
    func maintainVehicle()
}

class Cleaner: Robot {}