1. Hotine, M.: 1969,Mathematical Geodesy, U. S. Government Printing Office, Washington DC, pp. 153?155.
2. Szebehely, V.: 1974, ?On the Determination of the Potential by Satellite Observations?, in E. Proverbio (ed.),Proceedings of the International Meeting on Earth's Rotations by Satellite Observations, The University of Cagliari, Bologna, Italy.