1. Froissart M., Phys. Rev.123, 1053 (1961).
2. Oehme,R.: Fermi Institute Report EFI 71-26 (1971). Phys. Rev. D4, 1485 (1972). The results of this paper have already been presented at the Amsterdam International Conference on Elementary Particles, June–July 1971.
3. Denisov,S.P., Donskov,S.V., Gorin,Yu.P., Petrukhin,A.I., Prokoshkin,Yu.D., Shuvalov,R. S., Stoyanova,D.A., Allaby,J.V., Giacomelly,G.: Serpukhov Report (to be published).
4. Oehme,R.: Phys. Rev. Letters18, 1222 (1967). This paper contains further references.
5. - Fermi Institute Report EFI 71-32 (1971), Vieweg Verlag (published in the Heisenberg-Festschrift). This paper contains further references.