Consider the following premises. S_15(a_15) <-> s. r_4 <-> s. forall x_15: R_15(x_15) -> S_15(x_15). ~r_4. Can we infer R_15(a_15) 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_4 <-> s, ~r_4 we can infer ~s via biconditional elimination. From S_15(a_15) <-> s, ~s we can infer ~S_15(a_15) via biconditional elimination. Finally, from R_15(a_15) -> S_15(a_15), ~S_15(a_15) we can infer ~R_15(a_15) via modus tollens, which contradicts R_15(a_15). Therefore, the answer is no.