1. Ergebnisse der Mathematik;E.M. Alfsen,1971
2. Bauer, H.: Theorems of Korovkin type for adapted spaces. Ann. Inst. Fourier (Grenoble)23, 245?260 (1973)
3. Bauer, H.: Approximationssatz und abstrakte R�nder. Math.-Phys. Semesterber.23, 141?173 (1976)
4. Berens, H., Lorentz, G.G.: Theorems of Korovkin type for positive linear operators on Banach lattices. In: Approximation Theory. Proceedings of an International Symposium (Austin 1973), pp. 1?30. Editor G.G. Lorentz. New York-London: Academic Press 1973
5. Bliedtner, J., Hansen, W.: Simplicial cones in potential theory. Invent. Math.29, 83?110 (1975)