Consider the following premises. u_3 <-> P_6(a_5). forall x_6: ~Q_6(x_6). forall x_6: P_6(x_6) -> Q_6(x_6). Can we infer ~u_3 from them?
 From forall x_6: P_6(x_6) -> Q_6(x_6), forall x_6: ~Q_6(x_6) we can infer forall x_6: ~P_6(x_6). From forall x_6: ~P_6(x_6) we can infer ~P_6(a_5). Finally, from u_3 <-> P_6(a_5), ~P_6(a_5) we can infer ~u_3. Therefore, the answer is yes.