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: r -> q. q -> t_4. u <-> t_4.
r -> t_4 can be inferred via the transitivity rule. u -> t_4 can be inferred via the biconditional elimination rule. t_4 -> u can be inferred via the biconditional elimination rule.