What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? s_1 <-> q_13. ~s_1. u <-> s. p_6 -> q_13. s -> p_6.
s -> q_13. s_1 -> q_13. u -> s. q_13 -> s_1. s -> u. ~q_13.