Neagu, N. and Popa, M. (2026) “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(1), pp. 98-116. doi: 10.36120/2587-3644.v21i1.98-116.