1. B. A. Voinov, Akust. Zh. 40, 935 (1994).
2. I. P. Getman and N. V. Kurbatova, Akust. Zh. 40, 581 (1994).
3. C. Saltzer, Discrete Potential Theory for Two-Dimensional Laplace and Poisson Difference Equations, Technical Report No. 4086 (National Advisory Committee on Aeronautics, 1958).
4. V. S. Ryaben’kii, Math. Nachr. 177, 251 (1996).
5. P.-G. Martinsson and G. J. Rodin, Proc. R. Soc. A 465, 2489 (2009).