Slyusarchuk, V. Y. “Conditions for the Existence of Bounded Solutions of Nonlinear Differential and Functional Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 62, no. 6, June 2010, pp. 837–846, https://umj.imath.kiev.ua/index.php/umj/article/view/2914.