RudenkoA. V. 2004. “Approximation of Densities of Absolutely Continuous Components of Measures in a Hilbert Space Using the Ornstein-Uhlenbeck Semigroup”. Ukrains’kyi Matematychnyi Zhurnal 56 (12), 1654-64. https://umj.imath.kiev.ua/index.php/umj/article/view/3872.