1. A. N. Tikhonov and V. Ya. Arsenin, Methods for Solving Ill-Posed Problems (Nauka, Moscow, 1979) [in Russian].
2. A. P. Norden, The Theory of Surfaces (Goztekhizdat, Moscow, 1956) [in Russian].
3. V. G. Maz’ya and B. A. Plamenevskii, “On the Pseudoanalyticity of Solutions of a Perturbed Polyharmonic Equation in R n,” in Scattering Theory and Oscillation Theory (Leningrad, 1979), No. 9, pp. 75–91 [in Russian].
4. G. H. Hardy, J. E. Littlewood, and G. Polya, Inequalities (Cambridge Univ. Press, Cambridge, 1934; Inostrannaya Literatura, Moscow, 1948).
5. L. Hörmander, Linear Partial Differential Operators (Mir, Moscow, 1965; Springer-Verlag, Berlin, 1969).