Kovalenko, I. N. 2000. “Estimation of the Intensity of the Flow of Nonmonotone Refusals in the Queuing System $(≤ λ) G M$”. Ukrains’kyi Matematychnyi Zhurnal 52 (9): 1219-25. https://umj.imath.kiev.ua/index.php/umj/article/view/4529.