Translate the following inference to logic notation: For all x, x_7 is a taxi driver or x_7 will not drink water. There is at least one x for which x_7 will drink water or x_7 is not a taxi driver. Therefore there is at least one x for which x_7 will drink water if and only if x_7 is a taxi driver.
forall x: P(x) or ~Q(x). exists x: Q(x) or ~P(x). Therefore exists x: Q(x) <-> P(x).