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_3 -> t. r -> t_3. t -> t_3. t or r.
r -> t can be inferred via the transitivity rule. t_3 can be inferred via the disjunction elimination rule. t_3 <-> t can be inferred via the biconditional introduction rule. t <-> t_3 can be inferred via the biconditional introduction rule.