Translate the following inference to logic notation: Barbara is playing squash. For all x, if x_8 plays squash, then x_8 is writing a letter. For all x, if x_8 writes a letter, then x_8 is playing squash. Therefore Barbara is writing a letter.
P(a). forall x: P(x) -> Q(x). forall x: Q(x) -> P(x). Therefore Q(a).