1. Weinberg, S., A Model of Leptons, Phys. Rev. Lett. Vol.19, pp.1264-1266, 1967.
2. Gell-Mann M., A schematic model of baryons and mesons, Physics Letters, Vol.8, pp.214-215, 1964.
3. Zweig, G., An SU(3) Model for Strong Interaction Symmetry and its Breaking, CERN Report No.8181/Th 8419, Vol.13, pp.508–509, February 1964.
4. Glashow, S. L. , Partial-symmetries of weak interactions, Nuclear Physics, Vol.22, pp.579-588, 1961.
5. Salam, A., and Ward, J. C. , On a gauge theory of elementary interactions, Nuovo Cim., Vol.19, pp.165-170, 1961.