Translate the following inference to logic notation: There is at least one x for which y_4 is a mechanic if and only if y_4 will read a book. For all x, if y_4 reads a book, then y_4 is a mechanic. For all x, y_4 is not a mechanic. Therefore there is at least one x for which y_4 will not read a book.
exists x: P(x) <-> Q(x). forall x: Q(x) -> P(x). forall x: ~P(x). Therefore exists x: ~Q(x).