What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? u <-> u_2. s -> u_2. p_1 -> s. r <-> p_1. ~u.
p_1 -> u_2. u -> u_2. r -> p_1. u_2 -> u. p_1 -> r. ~u_2.