Mazhuga YI. Operator methods in the problem of estimating the asymptotics of the time of the first hit for the birth and death process. Ukr. Mat. Zhurn. [Internet]. 1993Aug.25 [cited 2024Nov.28];45(8):1104–1108. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/5906