1. Intuitionistic fuzzy sets
2. Z. Cen, Neural, Parallel, and Scientific Computations, 16(3), pp. 303–308, (2008).
3. R.J. Hussain, P.S. Kumar, Int J Syst Assur Eng Manag, (2014).
4. A. Mahmoodirad, T. Allahviranloo, S. Niroomand, Springer-Verlag GmbH Germany, (2018).
5. R.E.O. Malley, Introduction to singular perturbations. Academic press, New York, (1974).