Lykova, O. B. “On the Reduction Principle in the Theory of Stability of Motion”.
Ukrains’kyi Matematychnyi Zhurnal
45, no. 12 (December 25, 1993): 1653–1660. Accessed April 7, 2025.
https://umj.imath.kiev.ua/index.php/umj/article/view/5973
.