Translate the following inference to logic notation: For all x, if x_3 were a soldier, then x_3 is a taxi driver. There is at least one x for which x_3 will write a letter or x_3 is a soldier. For all x, x_3 will write a letter if and only if x_3 is a taxi driver. Therefore there is at least one x for which x_3 is a taxi driver.
forall x: P(x) -> Q(x). exists x: R(x) or P(x). forall x: R(x) <-> Q(x). Therefore exists x: Q(x).