What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? ~R_21(a_21). S_21(a_21) <-> q_13. forall x_21: R_21(x_21) <-> S_21(x_21).
S_21(a_21) -> q_13. q_13 -> S_21(a_21). forall x_21: R_21(x_21) -> S_21(x_21). forall x_21: S_21(x_21) -> R_21(x_21).