S. B. Hembars'ka and P. V. Zaderei, “On the absolute convergence of power series”, Ukr. Mat. Zhurn., vol. 51, no. 5, pp. 594–602, May 1999, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4647