Abdulkareem, Noor Abdulameer, et al. “Oscillation and Asymptotic Behavior of Solution of Nth Order System Nonlinear of Neutral Differential Equation”. Journal of Al-Qadisiyah for Computer Science and Mathematics, vol. 12, no. 1, Feb. 2020, pp. Math Page 72 – 82, doi:10.29304/jqcm.2020.12.1.669.