1. E. Fermi, Progr. Theor. Phys. 4 (1950) 570; Phys. Rev. 81 (1950) 115; ibid 92 (1953) 452; L.D. Landau, Izv. AN SSSR 17 (1953) 85.
2. A.N. Sissakian, L.A. Slepchenko, Preprint JINR, P2-10651, 1977; A.N. Sissakian, L.A. Slepchenko, Fizika 10 (1978) 21; S.Ch. Mavrodiev, V.K. Mitryushkin, A.N. Sissakian, H.T. Torosyan, Sov. Yad. Phys. 30 (1979) 245.
3. J. Manjavidze, JINR Report P2-88-724, 1988.
4. R. Feynman, Phys. Rev. Lett. 23 (1969) 1415; A.A. Logunov, M.A. Mestvirishvili, CERN TH/1659; A.A. Logunov, M.A. Mestvirishvili, Nguen Van Hieu, Phys. Lett. 25 B (1967) 611; A.A. Logunov, M.A. Mestvirishvili, CERN, TH-1707, 1973.
5. T.H. Burnett et al. (JACEE), Phys. Rev. Lett. 50 (1983) 2062; M. Adamus et al. (NA22), Phys. Lett. B 185 (1987) 200.