Translate the following inference to logic notation: For all x, x_7 is a janitor if and only if x_7 will play squash. There is at least one x for which if x_7 plays tennis, then x_7 is a janitor. For all x, x_7 will not play squash. Therefore there is at least one x for which x_7 will not play tennis.
forall x: P(x) <-> Q(x). exists x: R(x) -> P(x). forall x: ~Q(x). Therefore exists x: ~R(x).