1.
Perestyuk NA, Feketa PV. On Preservation of the Invariant torus for Multifrequency Systems. Ukr. Mat. Zhurn. [Internet]. 2013 Nov. 25 [cited 2025 Dec. 5];65(11):1498–1505. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/2529