1. G. Cocconi:Proceedings of the Moscow Cosmic Ray Conference, Vol.2 (Moscow, 1959), p. 327.
2. G. T. Zatsepin andA. E. Chudakov:Sov. Phys. JETP,41, 655 (1961).
3. A. E. Chudakov, V. L. Dadykin, V. I. Zastepin andN. M. Nesterova:Nukleonika,9, 347 (1964).
4. Proceedings of the International Workshop on Very High Energy Gamma-Ray Astronomy, Ootacamund, India, edited byP. V. Ramana Murthy andT. C. Weekes (Tata Institute of Fundamental Research and Smithsonian Institution, 1982).
5. C. Morello, G. Navarra andS. Vernetto:Proceedings of the XVIII International Cosmic Ray Conference, Vol.1 (Bangalore, 1983), p. 127.