1. F. J. Gilman: Rapporteur talk at theXVII International Conference on High-Energy Physics (London, 1974) and SLAC-PUB-1455.
2. E. M. Rirodan, A. Bodek, M. Breidenbach, D. L. Dubin, J. E. Elias, J. I. Friedman, H. W. Kendall, J. S. Poucher, M. R. Sogard andD. H. Coward:Phys. Rev. Lett.,33, 561 (1974).
3. R. P. Feynman:Photon-Hadron Interactions (New York, N. Y., 1972).
4. W. Chinowsky: Talk at theIV International Conference on Experimental Meson Spectroscopy, Northeastern University (1974);
5. B. Richter: Talk at theXVII International Conference on High-Energy Physics (London, 1974).