Fuzzy set theory has been studied a lot and applied to many diverse areas. For
examples, Brown [1] considered a note on fuzzy sets to obtain some analytical findings
on convex fuzzy sets, star-shaped fuzzy sets, and arcwise connected fuzzy sets.
Mizumoto and Tanaka [7] found some properties o f fuzzy sets for intuitive fuzzy sets.
They applied the extension principle to show that convex fuzzy grades form a
commutative semi-ring and normal convex fuzzy grades form a distributive lattice under
join and meet. Cheng [2] developed a new approach for ranking fuzzy numbers to
calculate the distance to the centroid point with the special characteristics: higher mean
and lower spread to incorporate with human intuition. Kumar et al. [3] investigated some
operations on intuitive fuzzy sets and then verified some propositions and provided some
examples. For medical diagnosis, Kumar et al. [4] presented an application of intuitive
fuzzy sets for decision making problems. Li [5] constructed multiattribute decision
making models under intuitive fuzzy sets environment to derive a pair of maximum and
minimum linear programming problems by combining two linear programming under the
same constraints.