1. Zadeh, LA., Fuzzy Sets, Information and Control, 8, 1965, pp. 338-353.
2. Voskoglou, M.Gr., Fuzzy Systems, Extensions and Relative Theories, WSEAS Transactions on Advances in Engineering Education, 16, 2019, pp. 63-69
3. Klir, G. J. & Folger, T. A., Fuzzy Sets, Uncertainty and Information, Prentice-Hall, London, 1988.
4. Deng, J., Introduction to Grey System Theory, The Journal of Grey System, 1, 1989, pp. 1-24.
5. Kharal, A. & Ahmad, B., Mappings on soft classes, New Mathematics and Natural Computation, 7(3), 2011, pp.471-481.