Y. I. Belopolskaya, A. A. Boitsev, S. Fassari, I. Y. Popov, and F. Rinaldi, “Two-dimensional Helmholtz resonator with two close point-like windows: regularization for the Neumann case”, MFAT, vol. 28, no. 2, pp. 95–104, Jun. 2022, doi: https://doi.org/10.31392/MFAT-npu26_2.2022.01.