EleikoY. I. “Limiting Distribution of Time Averages for the Additive Functionals Preset on the Semi-Markovian Process”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 42, no. 6, June 1990, pp. 843-7, https://umj.imath.kiev.ua/index.php/umj/article/view/8850.