Translate the following inference to logic notation: For all x, if z were a taxi driver, then z is taking a plane. For all x, if z takes a plane, then z is a taxi driver. Robert is not taking a plane. If Robert were not a taxi driver, then it is overcast. Therefore it is overcast.
forall x: P(x) -> Q(x). forall x: Q(x) -> P(x). ~Q(a). ~P(a) -> p. Therefore p.