1. Afanasiev, B.N., et al.: Proceedings of the International Symposium on Extremely High Energy Cosmic Rays: Astrophysics and Future Observatories, M. Nagano, ed., Institute for Cosmic Ray Research, University of Tokyo, p. 32 (1996).
2. Aglietta, M., et al.: Astropart. Phys., 10, p. 1 (1999).
3. Aguirre, C., et al.: PICRC, 4, p. 2592 (1973).
4. Aguirre, C., et al.: J. Phys. G, 5, p. 139 (1979).
5. Allan, H.R., et al.: Proc. Phys. Soc., 76, p. 1 (1960).