Translate the following inference to logic notation: There is at least one x for which x_9 is sad if and only if x_9 will make tea. For all x, x_9 is sad. For all x, x_9 will not make tea. Therefore there is at least one x for which x_9 will play tennis.
exists x: P(x) <-> Q(x). forall x: P(x). forall x: ~Q(x). Therefore exists x: R(x).