1. Dubois D, Prade H (1988) Possibility theory. Plenum Press, New York, NY, USA
2. Dubois D, Prade H (2007) Possibility theory. Scholarpedia 2(10):2074
3. Klawonn F, Castro JL (1995) Similarity in fuzzy reasoning. Mathware Soft Comput 2:197–228. University of Granada, Granada, Spain
4. Klawonn F (1994) Fuzzy sets and vague environment. Fuzzy Sets Syst 66:207–221. Elsevier, Amsterdam, Netherlands
5. Kruse R, Gebhardt J, Klawonn F (1994) Foundations of fuzzy systems. Wiley, Chichester, United Kingdom