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_21(a_21) -> q_9. P_21(a_21) or ~q_9. forall x_21: P_21(x_21).
q_9 -> P_21(a_21) can be inferred via the rewriting rule.