It is shown that Extensive Air Shower (EAS) longitudinal development has a critical point where an equilibrium between the main hadronic component and the secondary electromagnetic one exhibits a brake. This results in a change of slope in quasi-power law function $N_{e}(Eo)$. The latter leads to a knee in the EAS size spectrum at primary energy of about 100 TeV/nucleon. Many ``strange experimental results can be successfully explained in the frames of current approach.
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