Translate the following inference to logic notation: For all x, x_11 will not take a plane. For all x, x_11 will work or x_11 is a server. For all x, x_11 will take a plane if and only if x_11 is a server. For all x, x_11 will not work or z_1 is sad. Therefore there is at least one x for which z_1 is sad.
forall x: ~P(x). forall x: Q(x) or R(x). forall x: P(x) <-> R(x). forall x: ~Q(x) or S(x). Therefore exists x: S(x).