[en] The neutrino interactions with production of three or even four leptons raised the question of the 'purity' of the neutrino beam. Other species of neutrino that the electron-neutrino or muon-neutrino were searched. An experiment performed at CERN with using the 400 GeV proton accelerator seems to have evidenced a nonconventional source of neutrinos that means of original parent particles. The experiment consisted in suppressing the parents K and π mesons, of usual neutrinos by beam dump