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_8 -> r. r_4 -> q_8. t_2 -> r. r -> t_2.
q_8 -> t_2 can be inferred via the transitivity rule. r_4 -> r can be inferred via the transitivity rule. t_2 <-> r can be inferred via the biconditional introduction rule. r <-> t_2 can be inferred via the biconditional introduction rule.