Vitrychenko, I.E. (2000) “On the functional polystability of certain essentially nonlinear nonautonomous differential systems”, Ukrains’kyi Matematychnyi Zhurnal, 52(2), pp. 197–207. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4408 (Accessed: 5 December 2025).