Translate the following inference to logic notation: There is at least one x for which x_4 is an artist or x_4 is poor. For all x, x_4 is an artist if and only if x_4 is sad. For all x, x_4 is not sad. Therefore there is at least one x for which x_4 is poor.
exists x: P(x) or Q(x). forall x: P(x) <-> R(x). forall x: ~R(x). Therefore exists x: Q(x).