Fomichev, V. V. “Level-Crossing Intensity for the Density of the Image of the Lebesgue Measure under the Action of a Brownian Stochastic Flow”. Ukrains’kyi Matematychnyi Zhurnal, vol. 69, no. 6, June 2017, pp. 803-22, https://umj.imath.kiev.ua/index.php/umj/article/view/1736.