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