Translate the following inference to logic notation: For all x, x_11 is a sailor if and only if x_11 will take a plane. For all x, x_11 will take a plane if and only if x_11 is a sailor. Therefore if Sarah were a sailor, then Sarah is taking a plane.
forall x: P(x) <-> Q(x). forall x: Q(x) <-> P(x). Therefore P(a) -> Q(a).