  We present here arguments in favor of the existence of the lightest lepton
and its neutrino. This new family with a fourth lepton flavor uncovered so far
unobserved universal properties of matter. The unity of the laws of their
nature admits the flavor symmetrical decays of the electron and proton.
Thereby, it predicts the new modes in the decays of the muon, tau lepton and
neutron. At the same time, in all these transitions, no conservation laws are
violated, confirming the availability in nature of a place for an additivity of
mass.
