Ardjouni, A., and A. Djoudi. “EXISTENCE OF POSITIVE PERIODIC SOLUTIONS FOR A NONLINEAR NEUTRAL DIFFERENCE EQUATION WITH VARIABLE DELAY”. Journal of Nonlinear Analysis and Optimization: Theory & Applications 4, no. 2 (August 12, 2013): 31-38. Accessed November 28, 2021. http://www.math.sci.nu.ac.th/ojs302/index.php/jnao/article/view/280.