  Cosmology cannot rule out the solution nu_mu <-> nu_s to the atmospheric
neutrino data and thus only Earth experiments will be able to give a definitive
answer. This conclusion holds when a generation of lepton number is taken into
account and one assumes that the sterile neutrino is also slightly mixed with
an eV-tau neutrino. This result cannot be spoiled by a chaotic generation of
lepton domains.
