Translate the following inference to logic notation: For all x, x_10 will take a plane if and only if x_10 is a sailor. There is at least one x for which x_10 is happy if and only if x_10 is a sailor. For all x, x_10 will take a plane. Therefore there is at least one x for which x_10 is a sailor.
forall x: P(x) <-> Q(x). exists x: R(x) <-> Q(x). forall x: P(x). Therefore exists x: Q(x).