Korolyuk, V. S., and Ya. M. Chabanyuk. 2002. “Stability of a Dynamical System With Semi-Markov Switchings under Conditions of Stability of the Averaged System”. Ukrains’kyi Matematychnyi Zhurnal 54 (2), 195-204. https://umj.imath.kiev.ua/index.php/umj/article/view/4055.