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An SO(18) grand unified theory is presented. All fermions belong to one irreducible 256-dimensional spinor representation. It is shown that (i) in a favorable case there are eight light and eight superheavy families, (ii) masses of neutrinos, superheavy fermions, and horizontal gauge bosons are correlated with each other, (iii) there are new charged-current processes, $B+L$ conserving and ΔL=2, and (iv) two types of symmetry breaking lead to orthogonal choices of scalars. In one case [SO(18{→}SU(9)...] scalars may be replaced by fermion composites. Other physical features are also discussed.
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Yasushi Fujimoto (1982) studied this question.
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