Consider the following premises. R_7(a_7) <-> u. forall x_7: R_7(x_7) <-> S_7(x_7). ~S_7(a_7). Can we infer u from them?
 From forall x_7: R_7(x_7) <-> S_7(x_7) we can infer R_7(a_7) <-> S_7(a_7). From R_7(a_7) <-> S_7(a_7), ~S_7(a_7) we can infer ~R_7(a_7). Finally, from R_7(a_7) <-> u, ~R_7(a_7) we can infer ~u, which contradicts u. Therefore, the answer is no.