What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? ~u. q <-> q_3. r_1 <-> q_3. u <-> r_1.
q -> q_3. r_1 -> q_3. u -> r_1. q_3 -> q. q_3 -> r_1. r_1 -> u. ~r_1.