Consider the following premises. forall x_23: ~Q_23(x_23). exists x_23: P_23(x_23) <-> Q_23(x_23). forall x_23: P_16(x_23) <-> P_23(x_23). forall x_23: P_16(x_23) <-> Q_6(x_23). forall x_23: U(x_23) -> Q_6(x_23). Can we infer exists x_23: ~U(x_23) from them?
 From exists x_23: P_23(x_23) <-> Q_23(x_23), forall x_23: ~Q_23(x_23) we can infer exists x_23: ~P_23(x_23). From forall x_23: P_16(x_23) <-> P_23(x_23), exists x_23: ~P_23(x_23) we can infer exists x_23: ~P_16(x_23). From forall x_23: P_16(x_23) <-> Q_6(x_23), exists x_23: ~P_16(x_23) we can infer exists x_23: ~Q_6(x_23). Finally, from forall x_23: U(x_23) -> Q_6(x_23), exists x_23: ~Q_6(x_23) we can infer exists x_23: ~U(x_23). Therefore, the answer is yes.