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