What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? r_4 -> r_1. ~r_4. r_1 -> r_4. p_2 -> q_2. ~q_2.
~r_1. ~p_2. ~r_4 and ~q_2. ~q_2 and ~r_4. r_4 <-> r_1. r_1 <-> r_4.