Aydi, H., and M. Berzig. “COINCIDENCE POINT THEOREMS IN HIGHER DIMENSION FOR NONLINEAR CONTRACTIONS”. Journal of Nonlinear Analysis and Optimization: Theory & Applications (JNAO), vol. 4, no. 1, Oct. 2012, pp. 53-64, https://ph03.tci-thaijo.org/index.php/jnao/article/view/2685.