Sikorsky YI, Tereshchenko NI. On construction of partial solutions for linear heterogeneous differential equations in the vicinity of an irregular singular point . Ukr. Mat. Zhurn. [Internet]. 1971Oct.26 [cited 2024Nov.24];23(6):807-12. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/8632