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