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: w <-> q_12. s. w -> ~q_16. q_12 or u_4. q_16.
~w can be inferred via the modus tollens rule. s and q_16 can be inferred via the conjunction rule. q_16 and s can be inferred via the conjunction rule. w -> q_12 can be inferred via the biconditional elimination rule. q_12 -> w can be inferred via the biconditional elimination rule.