Consider the following premises. s <-> S_7(a). ~R_7(a). forall x_7: R_7(x_7) <-> S_7(x_7). Can we infer ~s from them? If possible, name the inference rules being used at each step.
 From forall x_7: R_7(x_7) <-> S_7(x_7) we can infer R_7(a) <-> S_7(a) via universal instantiation. From R_7(a) <-> S_7(a), ~R_7(a) we can infer ~S_7(a) via biconditional elimination. Finally, from s <-> S_7(a), ~S_7(a) we can infer ~s via biconditional elimination. Therefore, the answer is yes.