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 -> w_4. p_4 -> q. w_4 -> q. ~w_4.
~q can be inferred via the modus tollens rule. q <-> w_4 can be inferred via the biconditional introduction rule. w_4 <-> q can be inferred via the biconditional introduction rule.