An extension of the left-right symmetric model has been constructed wh
ich gives in a natural way the three lepton decay modes of the proton
which have been suggested as an explanation for the atmospheric neutri
no 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.