On the existence and asymptotics of a periodic solution of a degenerate singularly perturbed system of differential equations in the case of multiple elementary divisors. Neliniini Kolyvannya, [S. l.], v. 5, n. 1, p. 123–141, 2002. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/207. Acesso em: 22 jan. 2026.