What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? forall x: ~S_1(x). exists x: U(x) or T(x). forall x: S_1(x) <-> U(x).
forall x: S_1(x) -> U(x). forall x: U(x) -> S_1(x). forall x: ~U(x).