Neagu, Natalia, and Mihail Popa. “SO(2,R)-Invariant Polynomials of a Differential System Which Are Involved in Solving the Stability Problem of Unperturbed Motion in the Case of a Center and a Focus”. Acta et Commentationes Exact and Natural Sciences 21, no. 1 (July 23, 2026): 98-116. Accessed September 21, 2026. https://revistaust.upsc.md/index.php/acta_exacte/article/view/1327.