Team, S. “Application of Fixed Point Theory in Metric Spaces: R. Bhardwaj, S.S. Rajput, R.N. Yadava”. Thai Journal of Mathematics, vol. 5, no. 2, Dec. 2007, pp. 253-9, https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/91.