This paper introduces the notions of the star operators of degree n, n⩾3, and studies properties of ERL(n, ∑), which is the closure of the class of finite languages under the operations, union, concatenation, and the star operators of degree at most n. For any n⩾3, ERL(n, ∑) is a subclass of context-sensitive languages, and the inclusion problem between ERL(n, ∑) and the class of context-free languages is incomparable.
