Translate the following inference to logic notation: There is at least one x for which x_7 is a doctor if and only if x_7 is a sailor. For all x, x_7 is a musician if and only if x_7 is an office clerk. For all x, x_7 is not a musician. For all x, x_7 is an office clerk if and only if x_7 is a doctor. Therefore there is at least one x for which x_7 is not a sailor.
exists x: P(x) <-> Q(x). forall x: R(x) <-> S(x). forall x: ~R(x). forall x: S(x) <-> P(x). Therefore exists x: ~Q(x).