Agarwal, P., and J. V. Manojlović. “Asymptotic Behavior of Positive Solutions of Fourth-Order Nonlinear Difference Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, no. 1, Jan. 2008, pp. 8–27, https://umj.imath.kiev.ua/index.php/umj/article/view/3134.