What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: r <-> s. q. p_2 -> r. ~s.
q and ~s can be inferred via the conjunction rule. ~s and q can be inferred via the conjunction rule. r -> s can be inferred via the biconditional elimination rule. s -> r can be inferred via the biconditional elimination rule. ~r can be inferred via the biconditional elimination rule.