Rahman, K., A. Ali, M. Shakeel, M. S. A. Khan, and M. Ullah. “Pythagorean Fuzzy Weighted Averaging Aggregation Operator and Its Application to Decision Making Theory”. The Nucleus, vol. 54, no. 3, Sept. 2017, pp. 190-6, http://www.thenucleuspak.org.pk/index.php/Nucleus/article/view/184.