Chandok, S., & Narang, T. D. (2010). Common fixed points and invariant approximation of $R$-subweakly commuting maps in convex metric spaces. Ukrains’kyi Matematychnyi Zhurnal, 62(10), 1367–1376. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/2961