1. M.B. Amelchakov et al., Proc. 27th ICRC, Hamburg, 3 (2001) 1267
2. I.I. Yashin et al., Proc. 29th ICRC, Pune, 6 (2005) 373
3. M.B.Amelchakov et al. Presented at NANP'05, Dubna, 2005. Phys. Atom. Nucl., 70 (2007), in press
4. 5. D. Heck et al. Forschungszentrum Karlsruhe Report, FZKA 6019, Karlsruhe, 1998