Consider the following premises. S_12(a) -> ~s_1. s_1. forall x_12: R_12(x_12) <-> S_12(x_12). Can we infer R_12(a) from them? If possible, name the inference rules being used at each step.
 From forall x_12: R_12(x_12) <-> S_12(x_12) we can infer R_12(a) <-> S_12(a) via universal instantiation. From R_12(a) <-> S_12(a) we can infer R_12(a) -> S_12(a) via biconditional elimination. From S_12(a) -> ~s_1, s_1 we can infer ~S_12(a) via modus tollens. Finally, from R_12(a) -> S_12(a), ~S_12(a) we can infer ~R_12(a) via modus tollens, which contradicts R_12(a). Therefore, the answer is no.