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_8. q_8 -> s_1. s_1 -> r.
q_8 -> r can be inferred via the transitivity rule. r -> q_8 can be inferred via the biconditional elimination rule. q_8 -> r can be inferred via the biconditional elimination rule.