Vitrychenko, I. E. “Functional Polystability of Some Nonautonomous Quasilinear Differential Systems”. Ukrains’kyi Matematychnyi Zhurnal 51, no. 7 (July 25, 1999): 989–995. Accessed May 10, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4688.