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 y: ~S(y). forall y: U(y) or ~S(y). forall y: U(y) -> S(y). exists y: S(y) -> U(y).
forall y: ~U(y) can be inferred via the universal modus tollens rule. forall y: S(y) -> U(y) can be inferred via the universal rewriting rule. exists y: S(y) <-> U(y) can be inferred via the existential biconditional introduction rule. exists y: U(y) <-> S(y) can be inferred via the existential biconditional introduction rule.