What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? r_4 <-> s_3. p_8 <-> r_4. ~s_3. u_2 -> p_8.
r_4 -> s_3. p_8 -> r_4. s_3 -> r_4. r_4 -> p_8. ~r_4.