Ardjouni, A. and Djoudi, A. (2013) “EXISTENCE OF POSITIVE PERIODIC SOLUTIONS FOR A NONLINEAR NEUTRAL DIFFERENCE EQUATION WITH VARIABLE DELAY”, Journal of Nonlinear Analysis and Optimization: Theory & Applications, 4(2), pp. 31-38. Available at: http://www.math.sci.nu.ac.th/ojs302/index.php/jnao/article/view/280 (Accessed: 30November2021).