Gradual Sets: An Approach to Fuzzy Sets

In the fuzzy theory of sets and groups, use α-levels is a standard to translate problems from crisp framework. Using strong α-levels, it possible establish one correspondence which makes doubly, gradual functorial treatment theory. The main result this paper identify class sets, respectively, with subcategories categories Set (0, 1], resp., Gr 1]. line, algebraic potential will be reached, in forthcoming papers.