On the existence of invariant tori of <i>M</i>-frequency oscillation systems and their stability. Neliniini Kolyvannya, [S. l.], v. 2, n. 1, p. 128–132, 1999. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/46. Acesso em: 22 jan. 2026.