VitrychenkoI. E. “Global λ-Stability of One Nonautonomous Quasilinear Second-Order Equation”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 54, no. 9, Sept. 2002, pp. 1172-89, https://umj.imath.kiev.ua/index.php/umj/article/view/4157.