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: w <-> u. s_1. ~u. u or ~w.
~w can be inferred via the disjunctive syllogism rule. s_1 and ~u can be inferred via the conjunction rule. ~u and s_1 can be inferred via the conjunction rule. w -> u can be inferred via the rewriting rule. w -> u can be inferred via the biconditional elimination rule. u -> w can be inferred via the biconditional elimination rule. ~w can be inferred via the biconditional elimination rule.