Translate the following inference to logic notation: There is at least one x for which x_9 will make tea if and only if x_9 is an electrician. For all x, x_9 will not make tea. For all x, x_9 is a mechanic if and only if x_9 is an electrician. Therefore there is at least one x for which x_9 is not a mechanic.
exists x: P(x) <-> Q(x). forall x: ~P(x). forall x: R(x) <-> Q(x). Therefore exists x: ~R(x).