Translate the following inference to logic notation: For all x, x_4 is a lawyer if and only if x_4 is a sailor. For all x, if x_4 were a sailor, then x_4 is a lawyer. There is at least one x for which x_4 is not a sailor. Therefore there is at least one x for which x_4 is not a lawyer.
forall x: P(x) <-> Q(x). forall x: Q(x) -> P(x). exists x: ~Q(x). Therefore exists x: ~P(x).