Asymptotic solutions of a linear system with a small parameter at the partial derivatives. Neliniini Kolyvannya, [S. l.], v. 13, n. 1, p. 30–38, 2010. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/548. Acesso em: 21 jan. 2026.