1. Fuzzy sets
2. Klaua, D. (1965) Über einen Ansatz zur mehrwertigen Mengenlehre. Monatsb. Deutsch. Akad. Wiss. Berlin 7, 859–876. A recent in-depth analysis of this paper has been provided by Gottwald, S. (2010). "An early approach toward graded identity and graded membership in set theory". Fuzzy Sets and Systems.
3. D. Dubois and H. Prade (1988) Fuzzy Sets and Systems. Academic Press, New York.
4. J. Singh, C. Singh, S. Kumar, Implementation of Fuzzy Logic on FORTRAN Coded Free Convection Around Vertical Tube, in: K. Deep, J.C. Bansal, K.N. Das, A.K. Lal, H. Garg, A.K. Nagar, M. Pant (Eds.), Part Adv. Intell. Syst. Comput. B. Ser. (AISC, Volume 546), Springer, Singapore, 2017: pp. 331–341.
5. G.J. Klir and B. Yuan, Fuzzy Sets and Fuzzy Logic: Theory and Applications. Prentice-Hall, Upper Saddle River, NJ, 1995.