1. See,e.g.,W. Heisenberg:Introduction to the Unified Field Theory of Elementary Particles (London, 1966), where the earlier work is cited.H. P. Dürr:Acta Phys. Austriaca, Suppl.,3, 3 (1966).
2. H. P. Dürr:Proceedings of the Symposium on Basic Questions in Elementary Particle Physics, MPI für Physik und Astrophysik (München, 1971), p. 118;Quanten und Felder (Braunschweig, 1971), p. 126.
3. H. Mitter:Nuovo Cimento,32, 1789 (1964).
4. K. L. Nagy:State Vector Spaces with Indefinite Metric in Quantum Field Theory (Budapest, 1966);S. Schlieder:Zeits. Naturf.,14 a, 448, 460, 555 (1960);
5. H. P. Dürr andE. Rudolph:Nuovo Cimento,62 A, 411 (1969);65 A, 423 (1970).