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 -> r_1. t -> q_2. r or q_2. t -> r_1. q_2 -> t.
q_2 -> r_1 can be inferred via the transitivity rule. t <-> q_2 can be inferred via the biconditional introduction rule. q_2 <-> t can be inferred via the biconditional introduction rule.