What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: q_19 -> s_1. r_1 and w. ~s_1. s_1 -> q_19.
~q_19 can be inferred via the modus tollens rule. r_1 can be inferred via the simplification rule. w can be inferred via the simplification rule. q_19 <-> s_1 can be inferred via the biconditional introduction rule. s_1 <-> q_19 can be inferred via the biconditional introduction rule.