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_15 -> r_1. r_1 -> p_15. p_15 <-> q_15. q_15 -> r_1.
q_15 -> p_15 can be inferred via the transitivity rule. q_15 -> p_15 can be inferred via the transitivity rule. p_15 -> q_15 can be inferred via the biconditional elimination rule. q_15 -> p_15 can be inferred via the biconditional elimination rule.