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: q_19 -> u. u -> q_19. ~w_1. ~q_19. w -> w_1.
~u can be inferred via the modus tollens rule. ~w can be inferred via the modus tollens rule. ~w_1 and ~q_19 can be inferred via the conjunction rule. ~q_19 and ~w_1 can be inferred via the conjunction rule. q_19 <-> u can be inferred via the biconditional introduction rule. u <-> q_19 can be inferred via the biconditional introduction rule.