Translate the following inference to logic notation: For all x, if x_11 works, then x_11 is playing tennis. For all x, if x_11 plays tennis, then x_11 is sad. For all x, x_11 will work if and only if x_11 is sad. Therefore if Charles were sad, then Charles is working.
forall x: P(x) -> Q(x). forall x: Q(x) -> R(x). forall x: P(x) <-> R(x). Therefore R(a) -> P(a).