1. Jungck G: Commuting mappings and fixed point. Am. Math. Mon. 1976, 83: 261-263. 10.2307/2318216
2. Sessa S: On a weak commutativity conditions of mappings in fixed point considerations. Publ. Inst. Math. (Belgr.) 1982,32(46):146-153.
3. Jungck G: Compatible mappings and common fixed points. Int. J. Math. Sci. 1986,9(4):771-779. 10.1155/S0161171286000935
4. Dhage BC: Generalized metric spaces and mappings with fixed point. Bull. Calcutta Math. Soc. 1992, 84: 329-336.
5. Mustafa Z, Sims B: Some remarks concerning D -metric spaces. In Proceedings of International Conference on Fixed Point Theory and Applications. Yokohama Publishers, Yokohama; 2004: Valencia, Spain, July 13-19 189-198. Valencia, Spain, July 13-19