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_2 -> w_2. s -> q_6. w_2 -> r_2. ~q_6. r_2 <-> s.
~s can be inferred via the modus tollens rule. r_2 <-> w_2 can be inferred via the biconditional introduction rule. w_2 <-> r_2 can be inferred via the biconditional introduction rule. r_2 -> s can be inferred via the biconditional elimination rule. s -> r_2 can be inferred via the biconditional elimination rule.