RuzhevichN. A. “On a Limit Theorem for an Additive Functional on a Nonrecurrent Markovian Chain”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 49, no. 2, Feb. 1997, pp. 262–271, https://umj.imath.kiev.ua/index.php/umj/article/view/5003.