What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? q_20 -> q. q -> ~p_15. p_15 and q_15. p -> q_20. q_20 -> p.
q_20 -> ~p_15. p -> q. p_15. q_15. p <-> q_20. q_20 <-> p.