Chandok, S., and T. D. Narang. “Common Fixed Points and Invariant Approximation of $R$-Subweakly Commuting Maps in Convex Metric Spaces”. Ukrains’kyi Matematychnyi Zhurnal 62, no. 10 (October 25, 2010): 1367–1376. Accessed April 17, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2961.