Translate the following inference to logic notation: For all x, if x_11 works, then x_11 is a server. For all x, x_11 will take a plane or x_11 is not a server. For all x, if x_11 takes a plane, then x_11 is working. For all x, if x_11 were a server, then x_11 is taking a plane. Therefore for all x, x_11 is a server if and only if x_11 will take a plane.
forall x: P(x) -> Q(x). forall x: R(x) or ~Q(x). forall x: R(x) -> P(x). forall x: Q(x) -> R(x). Therefore forall x: Q(x) <-> R(x).