Denisova I. Y. “Reachability and Stability of Invariant Set of a System of Stochastic Differential Equations ”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 44, no. 4, Apr. 1992, pp. 568-72, https://umj.imath.kiev.ua/index.php/umj/article/view/7903.