1. S. M. Berman andM. Jacob:Phys. Rev. Lett.,25, 1678 (1970);S. M. Berman, J. D. Bjorken andJ. B. Kogut:Phys. Rev. D,4, 3388 (1971);S. D. Ellis andM. Kislinger:Phys. Rev. D,9, 2027 (1974).
2. M. Jacob andP. V. Landshoff:Phys. Rep.,48, 286 (1978).
3. M. Figgon andE. Predazzi:Z. Phys. C,1, 87 (1979).
4. M. Jacob andP. V. Landshoff:Phys. Rep.,48, 293 (1978), flg. 2.1.
5. B. Wiik: FERMILABSummerscchool Lectures on High Energy Accelerators, Batavia, Ill., U.S.A., July 9–24, 1981, and private conversation.