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3. F. M. Morse and G. Feshbach, Methods of Theoretical Physics [Russian translation], Vol. 2, IL, Moscow (1966), p. 273; Vol. 1 p. 480.
4. E. Pinney, J. Math. and Physics,25, 49 (1946).
5. G. Bateman and A. Erdein, Higher Transcendental Functions [Russian translation], Vol. 2, Nauka, Moscow (1966).