SIKORSKY, Yu. I.; TERESHCHENKO, N. I. On construction of partial solutions for linear heterogeneous differential equations in the vicinity of an irregular singular point . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 23, n. 6, p. 807–812, 1971. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8632. Acesso em: 5 dec. 2025.