1. M. A. Meyer, R. W. Wolfendale, E. B. Hughes andP. L. Marsden:Proc. Phys. Soc.,83, 239, 253 (1964).
2. O. O. Allkofer andR. D. Andresen:Nucl. Phys.,8 B, 402 (1968);Proceedings of the International Conference on Cosmic Rays, MU 1/2 (Budapest, 1969).
3. J. R. Hook, J. A. Jenkins andK. E. Turver:Proceedings of the International Conference on Cosmic Rays, MU 34 (Hobart, 1971).
4. A. M. Short:Proceedings of the International Conference on Cosmic Rays (London, 1965), p. 1006.
5. G. V. Gorshow, V. A. Zyabkin andR. M. Yakovlev:Soc. Journ. Nucl. Phys.,13, 450 (1971).