I. I. Yezhov, V. F. Kadankov, and T. V. Kadankova, “Two-boundary problems for a random walk”, Ukr. Mat. Zhurn., vol. 59, no. 11, pp. 1485–1509, Nov. 2007, Accessed: Apr. 09, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3406