1. Berg, C.: On the support of the measures in a symmetric convolution semigroup. To appear in Math. Z.
2. Erg. der Math.;C. Berg,1975
3. Bliedtner, J.: Harmonische Gruppen and Huntsche Faltungskerne. In: Lecture Notes in Mathematics no. 69. Berlin-Heidelberg-New York: Springer 1968
4. Bliedtner, J.: On the analytic structure of harmonic groups. Manuscripta Math.1, 289?292 (1969)
5. Pure and Applied Mathematics;R. M. Blumenthal,1968