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