What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? ~r_11. p_18 <-> q_18. p_18 <-> q_4. q_18 -> r_11.
~q_18. p_18 -> q_18. p_18 -> q_4. q_18 -> p_18. q_4 -> p_18.