1. P. K. F. Grieder:Acta Phys. Acad. Sci. Hung.,29, Suppl. 3, 569 (1970).
2. G. T. Murthy, K. Sivaprasad, M. V. Srinivasa Rao, S. C. Tonwar, R. H. Vatcha andP. R. Vishwanath:Can. Journ. Phys.,46, S 159 (1968).
3. S. C. Tonwar, S. Naranan andB. V. Sreekantan:Lett. Nuovo Cimento,1, 531 (1971).
4. B. Alper, H. Boggild, P. Booth, F. Bulos, L. J. Carroll, G. Damgaard, G. von Dardel, B. Duff, F. F. Heymann, J. N. Jackson, G. Jarlskog, L. Jönsson, A. Klovning, L. Leistam, E. Lillethun, G. Lynch, M. Prentice, D. Quarrie andJ. Weiss:Proceedings of the XVI International Conferences on High-Energy Physics (Batavia, Ill., 1972).
5. For a current account of the experimental situation, the reader is referred to theProceedings of the XIV International Cosmic Ray Conference, Vol.8 and12 (Munich, 1975), and references cited therein.