Shapeev, V. P. ., L. S. . Bryndin, and V. A. Belyaev. “Numerical Solution of an Elliptic Problem With Several Interfaces”. Numerical Methods and Programming (Vychislitel’nye Metody I Programmirovanie), vol. 23, no. 73, July 2022, pp. 172-90, doi:10.26089/NumMet.v23r311.