1. S. Drell andT. Yan:Phys. Rev. Lett.,24, 855 (1971);P. Landshoff andJ. Polkinghorne:Nucl. Phys.,33 B, 221 (1971);J. Stack:Phys. Rev. Lett.,28, 57 (1972);S. M. Berman, J. D. Bjorken andJ. B. Kogut:Phys. Rev. D,4, 3388 (1971);R. Feyman:Photon-Hadron Interactions (New York, N. Y., 1972).
2. The results of SLAC, Fermilab, Cornell and DESY experiments were reported byR. F. Mozley, L. Mo, K. M. Hanson andV. Eckardt, respectively, in theProceedings of the 1975 International Symposium on Lepton and Hadron Interactions at High Energies, edited byW. Kirk (Stanford, Cal., 1976). See also the report byG. Wolf in the same proceedings.
3. C. Heusch: UCSC-76/051 (June 1976);
4. J. F. Martin et al.: Stanford Linear Accelerator Center preprint SLAC-PUB-1766 (June 1976).
5. K. Bardakci andN. K. Pak:Lett. Nuovo Cimento,4, 719 (1972);N. K. Pak: University of California, Berkeley, Ph. D. Thesis (1972, unpublished).