Translate the following inference to logic notation: For all x, if z_3 were sad, then z_3 is driving a car. For all x, if z_3 drives a car, then z_3 is sad. There is at least one x for which if z_3 were sad, then z_3 is a mechanic. For all x, z_3 is not a mechanic. Therefore there is at least one x for which z_3 will not drive a car.
forall x: P(x) -> Q(x). forall x: Q(x) -> P(x). exists x: P(x) -> R(x). forall x: ~R(x). Therefore exists x: ~Q(x).