We derive the corrections induced by the W-boson propagator to the
differential rates of the leptonic decay of a polarized muon and tau lepton.
Results are presented both for decays inclusive of inner bremsstrahlung as well
as for radiative ones, when a photon emitted in the decay process is measured.
The numerical effect of these corrections is discussed. The definition of the
Fermi constant is briefly reviewed.Comment: 5 pages, no figures, accepted for publicatio
