Translate the following inference to logic notation: For all x, if z plays squash, then z is a taxi driver. For all x, if z were a taxi driver, then z is playing squash. There is at least one x for which z will play squash or z is not a taxi driver. Therefore there is at least one x for which if z were a taxi driver, then z is playing squash.
forall x: P(x) -> Q(x). forall x: Q(x) -> P(x). exists x: P(x) or ~Q(x). Therefore exists x: Q(x) -> P(x).