Dobrotin N.A. , Zacepin G.T. , Nikol'skij S.I. Interaction of ultra high energy particles with Nucleons and Atomic Nuclei. Nuovo Cimento , Suppl.,Ser.X,Vol.3,N4 , с. P.635-651 , 01.1956 Dobrotin N.A. , Zacepin G.T. , Chudakov A.E. , Grigorov N.L. , Vernov S.N. Investigation of interaction at extremely high-energies using the analysis of extensive air showers. Nuovo Cimento , Vol.8,suppl.N2 , с. P.737-741 , 01.1958