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: ~S_20(a_20). ~P_4(a_20) -> q. s. forall x_20: P_4(x_20) <-> S_20(x_20).
~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: P_4(x_20) -> S_20(x_20) can be inferred via the universal biconditional elimination rule. forall x_20: S_20(x_20) -> P_4(x_20) can be inferred via the universal biconditional elimination rule.