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: forall x_15: P_15(x_15) -> R_8(x_15). forall x_15: P_15(x_15) <-> S(x_15). forall x_15: ~R_8(x_15). exists x_15: S(x_15).
forall x_15: ~P_15(x_15) can be inferred via the universal modus tollens rule. forall x_15: P_15(x_15) -> S(x_15) can be inferred via the universal biconditional elimination rule. forall x_15: S(x_15) -> P_15(x_15) can be inferred via the universal biconditional elimination rule.