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3. Anderle, R.: 1965, ?Observations of Resonance Effects on Satellite Orbits Arising from the Thirteenth- and Fourteenth-Order Tesseral Gravitational Coefficients?,J. Geophys. Res. 70, No. 10.
4. Köhnlein, W.: ?The Earth's Gravitational Field as Derived from a Combination of Satellite Data with Gravity Anomalies?, prepared for the XIV General Assembly International Union of Geodesy and Geophysics, International Association of Geodesy, Lucerne, Switzerland, October 1967.
5. Rapp, R. H.: ?The Geopotential to (14, 14) from a combination of Satellite and Gravimetric Data?, presented at the XIV General Assembly International Union of Geodesy and Geophysics, International Association of Geodesy, Lucerne, Switzerland, October 1967.