ABSTRACT
The solutions of an important functional equation arising from information theory may be characterized using the concept of ordinal sum (Frank's theorem). Frank's theorem will be used in chapter 2 to prove the uniqueness of the pair (T00 , 800 ). Other topics of this chapter are:
• conditions for the uniqueness of the standard set connectives T0 , So;
• axiomatic definition of fuzzy complement;
• generator of a fuzzy complement;
• C-dual connectives;
• equilibrium and dual point of a complement.
