  In a supersymmetric SU(5) grand unified model with a horizontal symmetry
SU(1,1), we discuss spontaneous generation of generations to produce three
chiral generations of quarks and leptons and one generation of higgses by using
one structure field with a half-integer spin of SU(1,1) and two structure
fields with integer spins. In particular, the colored higgses can disappear
without fine-tuning. The difference of the Yukawa coupling matrices between the
down-type quarks and charged leptons is discussed. We show that some special
SU(1,1) weight assignments include R-parity as a discrete subgroup, and
R-parity remains even after we take into account the SU(1,1) breaking effects
from all the VEVs of the structure and matter fields. The assignments forbid
the baryon and/or lepton number violating terms except a superpotential quartic
term including a coupling of two lepton doublets and two up-type higgses. We
discuss how to generate sizable neutrino masses. We show that the proton decay
derived from the colored higgses is highly suppressed.
