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 or ~r_3. s_4 or r_3. s_1 -> r. s_4 -> s_1.
s_4 -> r can be inferred via the transitivity rule. r_3 -> r can be inferred via the rewriting rule.