MikhailetsV. A., and MurachA. A. “Regular Elliptic Boundary-Value Problem for a Homogeneous Equation in a Two-Sided Improved Scale of Spaces”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 58, no. 11, Nov. 2006, pp. 1536–1555, https://umj.imath.kiev.ua/index.php/umj/article/view/3553.