Translate the following inference to logic notation: There is at least one x for which z is a writer if and only if z is a taxi driver. For all x, z is a taxi driver if and only if z is a writer. Therefore there is at least one x for which z is a taxi driver if and only if z is a writer.
exists x: P(x) <-> Q(x). forall x: Q(x) <-> P(x). Therefore exists x: Q(x) <-> P(x).