Consider the following premises. R_15(a_15) or ~u. ~S_15(a_15). forall x_15: R_15(x_15) -> S_15(x_15). Can we infer ~u from them? If possible, name the inference rules being used at each step.
 From forall x_15: R_15(x_15) -> S_15(x_15) we can infer R_15(a_15) -> S_15(a_15) via universal instantiation. From R_15(a_15) -> S_15(a_15), ~S_15(a_15) we can infer ~R_15(a_15) via modus tollens. From R_15(a_15) or ~u we can infer u -> R_15(a_15) via rewriting. Finally, from u -> R_15(a_15), ~R_15(a_15) we can infer ~u via modus tollens. Therefore, the answer is yes.