PogoruiA. О. “Stationary Distribution of a Process of Random Semi-Markov Evolution With Delaying Screens in the Case of Balance”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, no. 3, Mar. 2006, pp. 381–387, https://umj.imath.kiev.ua/index.php/umj/article/view/3461.