Team, S. “The Common Fixed Point Theorems for Six Self-Mappings With Twice Power Type \Phi-Contraction Condition: Feng Gu, Dan Zhang”. Thai Journal of Mathematics, vol. 10, no. 3, Dec. 2012, pp. 587-03, https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/343.