  An extension of the left--right symmetric model has been constructed which
gives in a natural way the three lepton decay modes of the proton which have
been suggested as an explanation for the atmospheric neutrino anomaly. We write
down the potential which after minimization gives the proper choice of the
Higgs spectrum. With this Higgs spectrum we then study the evolution of the
gauge coupling constants and point out that for consistency one has to include
effects of gravity.
