Vitrychenko, I.E. (2005) “On a special critical case of stability of a nonautonomous essentially nonlinear system”,
Ukrains’kyi Matematychnyi Zhurnal, 57(12), pp. 1711–1718. Available at:
https://umj.imath.kiev.ua/index.php/umj/article/view/3721 (Accessed: 10 April 2025).