Translate the following inference to logic notation: For all x, y is sad or y will not play squash. For all x, if y plays squash, then y is sad. For all x, if y were sad, then y is playing squash. Therefore for all x, y will play squash if and only if y is sad.
forall x: P(x) or ~Q(x). forall x: Q(x) -> P(x). forall x: P(x) -> Q(x). Therefore forall x: Q(x) <-> P(x).