Fuzzy subsethood for Type-n fuzzy sets

Subsethood is the degree of containment of one fuzzy set in another, usually expressed as a value in the unit interval. We extend Kosko's definition of subsethood to Type-n fuzzy sets, for which subsethood is a Type-(n-l) fuzzy set on the unit interval. We then show how to compute subsethood for general Type-2 and interval Type-3 fuzzy sets.