Kovalev A, Nespirnyy V. Method of additional functions in stability theory for nonautonomous systems of differential equations . Dopov. Nac. akad. nauk Ukr. [Internet]. 2025 Mar. 1 [cited 2026 May 10];(8):20-7. Available from: https://nasu-periodicals.org.ua/index.php/dp/article/view/16605