: Membership function of the fuzzy set . X: Referential set. I: Valuation set. : Set of real numbers. : Set of all fuzzy sets from X to I. : α-cut of a fuzzy set . : Strong α-cut of a fuzzy set . : For all. : There exist. : Complement of a fuzzy set . : Intersection of two fuzzy sets and . : Union of two fuzzy sets and . : Classical solution. : Extension Principle solution. : α-cut and interval arithmetic solution. |