E. M. Saak, “On the regular approximation of the solutions of complex elliptical equations of any order”, Ukr. Mat. Zhurn., vol. 18, no. 6, pp. 26–40, Oct. 1966, Accessed: Apr. 07, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/8457