Slyusarchuk, V. Y. “Method of Local Linear Approximation in the Theory of Bounded Solutions of Nonlinear Differential Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 61, no. 11, Nov. 2009, pp. 1541-56, https://umj.imath.kiev.ua/index.php/umj/article/view/3120.