Choudhury, B. S., and A. Kundu. “FIXED POINT THEOREMS FOR NONLINEAR CONTRACTIONS IN ORDERED PARTIAL METRIC SPACES”. Journal of Nonlinear Analysis and Optimization: Theory & Applications 4, no. 1 (October 20, 2012): 147-158. Accessed December 9, 2021. http://www.math.sci.nu.ac.th/ojs302/index.php/jnao/article/view/187.