Translate the following inference to logic notation: There is at least one x for which if x_6 were a doctor, then x_6 is a janitor. For all x, x_6 is a doctor if and only if x_6 is a janitor. For all x, x_6 is not a doctor. Therefore there is at least one x for which x_6 is not a janitor.
exists x: P(x) -> Q(x). forall x: P(x) <-> Q(x). forall x: ~P(x). Therefore exists x: ~Q(x).