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. ~r_4 -> q. r_4 <-> t. ~t.
~r_4 -> w can be inferred via the transitivity rule. r_4 -> t can be inferred via the biconditional elimination rule. t -> r_4 can be inferred via the biconditional elimination rule. ~r_4 can be inferred via the biconditional elimination rule.