a wheel and axle is a kind of simple machine
wagon_wheel is wheel. wheel is not machine. wheel_and_axle is not mechanical_device. wheel_and_axle is vehicle_part. wheels_must has axle most_wheeled_vehicles has kind_of_axle wheel_and_axle is mechanical_device. wheel is machine. wheel_and_axle is not vehicle_part. live_axle is axle.