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: ~u_2. ~w_4. p -> u_2. w_4 -> p_19. p_19 -> w_4.
~p can be inferred via the modus tollens rule. ~p_19 can be inferred via the modus tollens rule. ~u_2 and ~w_4 can be inferred via the conjunction rule. ~w_4 and ~u_2 can be inferred via the conjunction rule. w_4 <-> p_19 can be inferred via the biconditional introduction rule. p_19 <-> w_4 can be inferred via the biconditional introduction rule.