Translate the following inference to logic notation: For all x, x_3 is a carpenter if and only if x_3 is a sailor. For all x, x_3 is sad. There is at least one x for which if x_3 were a sailor, then x_3 is not sad. Therefore there is at least one x for which x_3 is not a carpenter.
forall x: P(x) <-> Q(x). forall x: R(x). exists x: Q(x) -> ~R(x). Therefore exists x: ~P(x).