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(a_20) -> u. ~S_20(a_20). forall x_20: W(x_20) <-> S_20(x_20). s.
~S_20(a_20) and s can be inferred via the conjunction rule. s and ~S_20(a_20) can be inferred via the conjunction rule. forall x_20: W(x_20) -> S_20(x_20) can be inferred via the universal biconditional elimination rule. forall x_20: S_20(x_20) -> W(x_20) can be inferred via the universal biconditional elimination rule.