On asymptotic expansion of solutions of systems of differential equations in the case where the characteristic equation has multiple roots. Neliniini Kolyvannya, [S. l.], v. 3, n. 2, p. 285–289, 2000. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/119. Acesso em: 22 jan. 2026.