What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? ~u_2 or u. u_2. ~r_4. r_4 <-> q_9.
u_2 and ~r_4. ~r_4 and u_2. r_4 -> q_9. q_9 -> r_4. ~q_9.