D. D. Padma Priya, G. Shobhalatha, and R. Bhuvana Vijaya. “Fuzzyfication of Semigroups”. International Journal of Mathematics And Its Applications, vol. 4, no. 2 - A, May 2016, pp. 79-83, https://ijmaa.in/index.php/ijmaa/article/view/1008.