  Extrapolating the coupling strengths to very high energies, one finds that
they do not converge to a single coupling constant, as expected in the simplest
gauge theory of Grand Unification, the SU(5) theory. We find that the coupling
constants do converge, provided that two new intermediate energy scales are
introduced, the energies where the group SU(4), containing the color group, and
the right-isospin gauge group are spontaneously broken down.
