Consider the following premises. S_12(a_12) -> u. ~u. q_4 <-> R_12(a_12). forall x_12: R_12(x_12) <-> S_12(x_12). Can we infer q_4 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_12) <-> S_12(a_12) via universal instantiation. From S_12(a_12) -> u, ~u we can infer ~S_12(a_12) via modus tollens. From R_12(a_12) <-> S_12(a_12), ~S_12(a_12) we can infer ~R_12(a_12) via biconditional elimination. Finally, from q_4 <-> R_12(a_12), ~R_12(a_12) we can infer ~q_4 via biconditional elimination, which contradicts q_4. Therefore, the answer is no.