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: p_20 -> w. p_20 -> ~q_11. q_11. p_20 <-> w.
~p_20 can be inferred via the modus tollens rule. p_20 -> w can be inferred via the biconditional elimination rule. w -> p_20 can be inferred via the biconditional elimination rule.