Translate the following inference to logic notation: There is at least one x for which x_4 is happy if and only if x_4 is sad. For all x, x_4 is happy. Therefore there is at least one x for which x_4 is sad or x_4 will play squash.
exists x: P(x) <-> Q(x). forall x: P(x). Therefore exists x: Q(x) or R(x).