What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? r -> r_21. p_21 -> r. q_17 -> r_17. q_3 or q_17. ~p_21. q_3 -> r_17. r_21 -> p_21.
~r_21. r -> p_21. p_21 -> r_21. r_21 -> r. r_17.