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2. Arnold, K.: Methoden der Satellitengeodäsie. Akad. Verlag, Berlin (1970)
3. Bullen, K.E., Bolt, B.A.: An Introduction to the Theory of Seismology, 4th edn. Cambridge University Press, Cambridge (1985)
4. Caputo, M.: The Gravity Field of the Earth from Classical and Modern Methods. Academic Press, New York (1967)
5. Chuikova, N.A.: On convergence of series in spherical harmonics representing the outer potential on the physical surface of a planet. Isvestia Vusov, ser. Geodesy 4, 53–54 (1980). (in Russian)