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: t -> r_4. ~w. t -> w. r_4 -> t.
~t can be inferred via the modus tollens rule. r_4 -> w can be inferred via the transitivity rule. t <-> r_4 can be inferred via the biconditional introduction rule. r_4 <-> t can be inferred via the biconditional introduction rule.