**8.6 Introduction
To Fuzzy Set Theory**

Fuzzy set is a "class" with a continuum of grades of membership (Zadeh, 1965). More often than not, the classes of objects encountered in the real physical world do not have precisely defined criteria of membership. For example, the "class of all real numbers which are much greater than 1", or the "class of beautiful cats", do not constitute classes or sets in the usual mathematical sense of these terms. However, the fact remains that such imprecisely defined "classes" pay an important role in human thinking, particularly in the domain of patterns recognition, and abstraction

8.6.2. Logical Operations of Ordinary Sets

8.6.3. Fuzzy Set, Its Definition and Arithmetic Operations

8.6.4. Transformations Between Fuzzy Sets and Ordinary Sets

8.6.7. Possibility Distribution

8.6.8. Algebraic Operations on Fuzzy Sets

8.6.9. A Proposed Procedure for Use of Fuzzy Set Theory in Integrated Analysis of Spatial Data