Translate the following inference to logic notation: There is at least one x for which x_3 will write a letter if and only if x_3 will read a book. For all x, x_3 is a taxi driver if and only if x_3 will write a letter. For all x, x_3 is not a taxi driver. Therefore there is at least one x for which x_3 will not read a book.
exists x: P(x) <-> Q(x). forall x: R(x) <-> P(x). forall x: ~R(x). Therefore exists x: ~Q(x).