  An extra $SU(2)_D$ gauge factor is added to the well-known left-right
extension of the standard model (SM) of quarks and leptons. Under $SU(2)_L
\times SU(2)_R \times SU(2)_D$, two fermion bidoublets $(2,1,2)$ and $(1,2,2)$
are assumed. The resulting model has an automatic dark $U(1)$ symmetry, in the
same way that the SM has automatic baryon and lepton $U(1)$ symmetries.
Phenomenological implications are discussed, as well as the possible origin of
this proposal.
