I. E. Vitrychenko, “On the functional polystability of certain essentially nonlinear nonautonomous differential systems”, Ukr. Mat. Zhurn., vol. 52, no. 2, pp. 197–207, Feb. 2000, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4408