Bratiichuk, M. S.; Chechelnitsky , A. A.; Usar, I. Y. M/M/1//Retrial/Queueing/Model/With/Variable/Service/Rate. Ukr. Mat. Zhurn. 2020, 72 (3), 355-365. https://doi.org/10.37863/umzh.v72i3.813.