  We proof that the proton is stable in the left-right symmetric gauge model
[SU(6)]$^3\times$Z$_3$, which unifies nongravitational forces with flavors,
broken spontaneously by a minimal set of Higgs Fields and Vacuum Expectation
Values down to SU(3)$_{c}\otimes$U(1)$_{EM}$\hspace{0.2cm} . We also compute
the evolution of the gauge coupling constants and show how agreement with
precision data can be obtained.
