1. L. V. Volkova andG. T. Zatsepin:Bull. Acad. Sci. USSR, Phys. Ser.,38, 151 (1974).b)I. P. Nedyalkov:Rep. Bulg. Acad. Sci.,33, 1615 (1980);34, 1495, (1981).c)A. De Rújula, S. L. Glashow, R. R. Wilson andG. Charpak:Phys. Rep.,99, 341 (1983). (*)|Unfortunately the author had no opportunity to read a paper byA. Placci andE. Zavattini (CERN report 1973) and knew of it only from references in other papers.
2. K. Mann andH. Primakoff: preprint of University of Pennsylvania (1976).b)P. Kotzer:Experimental Proposal to Fermi National Accelerator Laboratory proposal No. 561 (1977).c)V. A. Tsarev andV. A. Chechin:Kratk. Soobshch. Fiz.,4, 8 (1982) (in Russian).
3. L. V. Volkova andG. T. Zatsepin:Sov. J. Nucl. Phys.,37, 212 (1983).
4. N. P. Zotov, V. A. Saleev, V. A. Tsarev andV. A. Chechin:Pis'ma Ž. Ėksp. Teor. Fiz.,39, 81 (1984) (in Russian).
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