1. Quarks models with integrally charged quarks escape this difficulty by assuming that quarks behave as ordinary hadrons do. SeeM. Y. Han andY. Nambu:Phys. Rev.,139, B 1006 (1965);
2. M. Y. Han andY. Nambu:Phys. Rev. D,10, 674 (1974).
3. A statistically significant sample of dynamical quark confinement mechanisms is reviewed inP. Ramond: invited talk at the APSMeeting in Williamsburg, Va., 1974, Yale University preprint, unpublished.
4. M. Günaydin andF. Gürsey:Lett. Nuovo Cimento,6, 401 (1973);Journ. Math. Phys.,14, 1651 (1973);Phys. Rev. D,9, 3387 (1974);F. Gürsey: inProceedings of the Johns Hopkins University Workshop, edited byG. Domokos andS. K. Domokos (Baltimore, Md., 1974); invited talk at theKyoto Conference, 1975, Yale University preprint (1975), unpublished. These papers will be referred to as Gj (1 ≤j≤5) in the order listed here.
5. See,e.g.,R. D. Schafer:An Introduction to Nonassociative Algebras, chap. V (New York, N. Y., 1966).