Consider the following premises. forall x_5: ~R_5(x_5). u <-> R_5(a_5). Can we infer ~u from them?
 From forall x_5: ~R_5(x_5) we can infer ~R_5(a_5). Finally, from u <-> R_5(a_5), ~R_5(a_5) we can infer ~u. Therefore, the answer is yes.