BogdanskiiY. V. “Cauchy Problem for an Essentially Infinite-Dimensional Parabolic Equation With Variable Coefficients”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 46, no. 6, June 1994, pp. 663–670, https://umj.imath.kiev.ua/index.php/umj/article/view/5693.