Translate the following inference to logic notation: For all x, x_15 is a taxi driver if and only if x_15 will write a letter. There is at least one x for which x_15 will write a letter. For all x, x_15 is a writer. Therefore there is at least one x for which x_15 is a taxi driver.
forall x: P(x) <-> Q(x). exists x: Q(x). forall x: R(x). Therefore exists x: P(x).