  Lepton asymmetry generated in the early universe by neutrino oscillations
into sterile partners is calculated. Kinetic equations are analytically reduced
to a simple form that permits an easy numerical treatment. Asymptotic values of
the asymmetry are at the level of 0.2-0.3 and are reasonably close to those
obtained by other groups, though the approach to asymptotics in some cases is
noticeably slower. No chaoticity is observed.
