1. F. Zachariasen: California Institute Technical preprint, CALTH-68-504 (1975).
2. H. I. Miettinen:Plenary Session Talk at the International Conference on High-Energy Physics,Palermo, 1975.
3. E. J. Squires:Nucl. Phys.,102 B, 93 (1976).
4. H. Harari:Phys. Lett.,51 B, 479 (1974).
5. J. Pumplin:Phys. Rev. D,8, 2899 (1973).