Translate the following inference to logic notation: For all x, x_5 is a taxi driver if and only if x_5 is sad. There is at least one x for which x_5 will cook or x_5 is a taxi driver. For all x, if x_5 were a janitor, then x_5 is sad. For all x, if x_5 cooks, then x_5 is a janitor. Therefore there is at least one x for which x_5 is sad.
forall x: P(x) <-> Q(x). exists x: R(x) or P(x). forall x: S(x) -> Q(x). forall x: R(x) -> S(x). Therefore exists x: Q(x).