What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? q_1 -> r_2. r -> ~q_18. r_2 -> q_1. t. q_18. r <-> r_2.
~r. t and q_18. q_18 and t. q_1 <-> r_2. r_2 <-> q_1. r -> r_2. r_2 -> r.