BogdanskiiY. V. “Dirichlet Problem for the Poisson Equation With an Essentially Infinite-Dimensional Elliptic Operator”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 46, no. 7, July 1994, pp. 803–808, https://umj.imath.kiev.ua/index.php/umj/article/view/5670.