Vovkodav, . N. G., & Shlepakov, . L. N. (2004). On the Optimal Coefficient of Efficiency of a Semi-Markov System in the Scheme of Phase Lumping. Ukrains’kyi Matematychnyi Zhurnal, 56(3), 339-345. https://umj.imath.kiev.ua/index.php/umj/article/view/3757