1. Friedrichs, K. O.: Mathematical aspects of the quantum theory of fields. New York: Interscience Publishers, Inc. 1953
2. Capri, A. Z.: J. Math. Phys.10, 575 (1969)
3. Schroer, B., Seiler, R., Swieca, J. A.: Phys. Rev.2D, 2927 (1970)
4. Seiler, R.: Commun. math. Phys.25, 127 (1972)
5. Shale, D.: Transact. Amer. Math. Soc.103, 149 (1962)