DaP. G. “Regularity Results for Kolmogorov Equations in $L^2 (H, μ)$ Spaces and Applications”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 49, no. 3, Mar. 1997, pp. 448–457, https://umj.imath.kiev.ua/index.php/umj/article/view/5017.