Translate the following inference to logic notation: For all x, if x_13 writes a letter, then x_13 is not driving a car. For all x, x_13 will play squash or x_13 is a scientist. For all x, if x_13 were a scientist, then x_13 is driving a car. There is at least one x for which x_13 will play squash if and only if x_13 will drive a car. Therefore there is at least one x for which x_13 will not write a letter.
forall x: P(x) -> ~Q(x). forall x: R(x) or S(x). forall x: S(x) -> Q(x). exists x: R(x) <-> Q(x). Therefore exists x: ~P(x).