PankovA. A., and PankovaT. E. “Iterative Reduction of the Dirichlet Problem to the Neumann Problem”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 47, no. 3, Mar. 1995, pp. 362–369, https://umj.imath.kiev.ua/index.php/umj/article/view/5425.