Consider the following premises. forall x_15: R_15(x_15) -> S_15(x_15). t_3 <-> S_15(a_15). ~u. u <-> t_3. Can we infer ~R_15(a_15) from them?
 From forall x_15: R_15(x_15) -> S_15(x_15) we can infer R_15(a_15) -> S_15(a_15). From u <-> t_3, ~u we can infer ~t_3. From t_3 <-> S_15(a_15), ~t_3 we can infer ~S_15(a_15). Finally, from R_15(a_15) -> S_15(a_15), ~S_15(a_15) we can infer ~R_15(a_15). Therefore, the answer is yes.