What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? forall x_8: P_8(x_8) -> S(x_8). forall x_8: S(x_8) -> P_8(x_8). forall x_8: S(x_8) -> P_8(x_8). ~P_8(a_2).
forall x_8: P_8(x_8) <-> S(x_8). forall x_8: P_8(x_8) <-> S(x_8). forall x_8: S(x_8) <-> P_8(x_8). forall x_8: S(x_8) <-> P_8(x_8).