What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? p_18 <-> q_4. p_18 <-> w_2. w_2 -> r_11. ~r_11.
~w_2. p_18 -> q_4. p_18 -> w_2. q_4 -> p_18. w_2 -> p_18.