1. I. M. Gel'fand and N. Ya. Vilenkin, Generalized Functions [in Russian], Vol. 4, Fizmatgiz (1961), Chapter 1.
2. M. A. Naimark, Normed Rings [in Russian], Gostekhizdat (1956), Chapter 4.
3. A. S. Wightman, Phys. Rev.,101, 860 (1956).
4. H. J. Borchers, Nuovo Cim.,24, 214 (1962).
5. R. Streater and A. Wightman, PCT, Spin, Statistics, and All That [Russian translation], Nauka (1966).