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 or r_20. p_4 -> r_15. p or p_4. r_15 -> q_1. r_20 -> r_15.
p_4 -> q_1 can be inferred via the transitivity rule. r_20 -> q_1 can be inferred via the transitivity rule. p_4 or r_20 can be inferred via the resolution rule.