Общество с ограниченной ответственностью Издательско-торговая корпорация "Дашков и К". 2018. 411 с.
The paper presents two incongruent flat simply connected domains with a visually smooth boundary for which the eigenvalues of the Dirichlet–Neumann operator, obtained using the algorithm cited in the paper, are practically identical. DOI 10.1134/S1061920825601107