Team, S. “Coupled Coincidence and Coupled Common Fixed Point Theorems in Partially Ordered Metric Spaces: Wutiphol Sintunavarat, Poom Kumam”. Thai Journal of Mathematics, vol. 10, no. 3, Dec. 2012, pp. 551-63, https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/340.