利用集合套理论，讨论了双枝模糊集普通并－分解，普通交－现定分解定理及相应的表理基础上的扩展原理的不同形式，以及复合函数的扩展原理。

• Using the theory of set cover, this paper discusses the different forms of extension principle based on the ordinary union-decomposition theorem, ordinary intersection-decomposition theorem and corresponding representation theorem in both-branch fuzzy sets , as well as the extension principle of composite function.