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_1 -> r. r_4 -> q_1. s or ~u. s -> r_4.
r_4 -> r can be inferred via the transitivity rule. s -> q_1 can be inferred via the transitivity rule. u -> s can be inferred via the rewriting rule.