Nguyen Tien Khiem. 1992. “A New Approach to Solution of the Focker-Plank-Kolmogorov Equation Tor Random Oscillatory Nonlinear Systems”. Ukrains’kyi Matematychnyi Zhurnal 44 (8), 1123-29. https://umj.imath.kiev.ua/index.php/umj/article/view/8045.