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: ~u_2. u_2 -> w_1. w_1 -> u_2. s.
~w_1 can be inferred via the modus tollens rule. ~u_2 and s can be inferred via the conjunction rule. s and ~u_2 can be inferred via the conjunction rule. u_2 <-> w_1 can be inferred via the biconditional introduction rule. w_1 <-> u_2 can be inferred via the biconditional introduction rule.