Asymptotic solutions of singularly perturbed linear differential system with an irregular singular point. Neliniini Kolyvannya, [S. l.], v. 12, n. 3, p. 417–432, 2009. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/535. Acesso em: 21 jan. 2026.