Goshko, L. V., and N. I. Portenko. “Limit Theorems for the Number of Crossings of a Fixed Plane by Certain Sequences of Generalized Dbffusion Processes”. Ukrains’kyi Matematychnyi Zhurnal, vol. 46, no. 4, Apr. 1994, pp. 357–371, https://umj.imath.kiev.ua/index.php/umj/article/view/5732.