1. A. Erdelyi (ed.), Higher Transcendental Functions, McGraw-Hill, New York (1953).
2. Yu. M. Berezanskii, ?Expansion of Self-adjoint Operators in Characteristic Functions? [in Russian], Naukova Dumka, Kiev (1965).
3. M. M. Vainberg and V. A. Trenogin, The Theory of Branching of Solutions to Nonlinear Equations [in Russian], Nauka, Moscow (1969).
4. V. S. Vladimirov, The Equations of Mathematical Physics [in Russian], Nauka, Moscow (1971).
5. S. A. Gabov, ?One problem on the hydrodynamics of an ideal liquid associated with flotation,? Differents. Uravnen.,24, No. 1, 16?21 (1988).