Team, S. “A Fixed Point Approach to the Generalized Hyers-Ulam Stability of Reciprocal Difference and Adjoint Functional Equations: K. Ravi, J.M. Rassias, B.V. Senthil Kumar”. Thai Journal of Mathematics, vol. 8, no. 3, Dec. 2010, pp. 469-81, https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/215.