1. Cimmino G (1955) Spazi hilbertiani di funzioni armoniche e questioni connesse. Equazioni lineari alle derivate parziali. Trieste 1954, UMI Roma
2. Gikhman AV, Skorokhod AV (2004) The theory of stochastic processes. Springer, Berlin
3. Krarup T (1969) A contribution to the mathematical fundation of physical geodesy. Meddelelse N44 Geodaetisk Institut, Kobehavn
4. Krarup T (1981) A convergence problem in collocation theory. Boll Geod Sci Affini 40: 225–240
5. Krarup T (1991) Approximation to the earth potential from discrete measurements. In: Proceedings of the Geodetic day in honour of A. Marussi. Atti Convegno Lincei, pp 67–85