KOVALEV, A.; NESPIRNYY, V. Method of additional functions in stability theory for nonautonomous systems of differential equations . Reports of the National Academy of Sciences of Ukraine, Kyiv, Ukraine, n. 8, p. 20–27, 2025. DOI: 10.15407/dopovidi2014.08.020. Disponível em: https://nasu-periodicals.org.ua/index.php/dp/article/view/16605. Acesso em: 10 may. 2026.