if something is zero shade during zero space and another shade during another time, then at something recessive shade
zero is digit. trivial_zero_divisor is zero_divisor. zero is not digit. when_car is parked_speed_zero. trivial_zero_divisor is not zero_divisor. shadow is not shade. shade is not color. space has not zero_pressure space has zero_pressure when_car is not parked_speed_zero.