What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? q_13 <-> r_4. u_3 <-> q_13. r_4 or w_4. ~u_3.
q_13 -> r_4. u_3 -> q_13. r_4 -> q_13. q_13 -> u_3. ~q_13.