On asymptotic expansions of solutions of a system of differential equations with slowly changing coefficients. Neliniini Kolyvannya, [S. l.], v. 5, n. 4, p. 549–559, 2002. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/241. Acesso em: 22 jan. 2026.