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: p -> s_4. s_4 -> u_1. u_1 -> r_1. p or ~s.
p -> u_1 can be inferred via the transitivity rule. s_4 -> r_1 can be inferred via the transitivity rule. s -> p can be inferred via the rewriting rule.