  We consider the spin polarization of leptons produced in neutrino and
antineutrino nucleon deep inelastic scattering, via charged currents, and we
study the positivity constraints on the spin components in a model independent
way. These results are very important, in particular in the case of
$\tau^{\pm}$ leptons, because the polarization information is crucial in all
future neutrino oscillation experiments.
