Translate the following inference to logic notation: For all x, if y_4 plays tennis, then y_4 is taking a plane. For all x, if y_4 takes a plane, then y_4 is playing tennis. James is not an electrician or Barbara is a writer. James is an electrician or Sarah is playing tennis. For all x, y_4 will not take a plane. Therefore Barbara is a writer.
forall x: P(x) -> Q(x). forall x: Q(x) -> P(x). ~p or q. p or P(a). forall x: ~Q(x). Therefore q.