On constructing a solution of a degenerate linear differential system of equations in a neighbourhood of an irregular singular point. Neliniini Kolyvannya, [S. l.], v. 7, n. 4, p. 555–561, 2004. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/329. Acesso em: 22 jan. 2026.