Translate the following inference to logic notation: There is at least one x for which if z_1 were a janitor, then z_1 is taking a plane. For all x, z_1 will take a plane if and only if z_1 will drive a car. For all x, z_1 will drive a car if and only if z_1 is a janitor. Therefore there is at least one x for which z_1 will drive a car if and only if z_1 will take a plane.
exists x: P(x) -> Q(x). forall x: Q(x) <-> R(x). forall x: R(x) <-> P(x). Therefore exists x: R(x) <-> Q(x).