Translate the following inference to logic notation: For all x, y will not write a letter. For all x, x_12 will read a book if and only if x_12 will drive a car. Sarah is writing a letter if and only if Barbara is driving a car. Therefore Barbara is not reading a book.
forall x: ~P(x). forall x: Q(x) <-> R(x). P(a) <-> R(b). Therefore ~Q(b).