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2. C. Rebbi: lectures at the1973 Erice Summer School, CERN preprint TH 1691 and references therein.
3. Y. Nambu:Dual models of hadrons, talk at theAPS Chicago Meeting, January 1970, EFI preprint COO-264-535.
4. M. Born:Ann. Inst. Poincaré, Vol.7, fasc. 4, 189 (1937) (in French) and references therein.
5. H. C. Tze:Lett. Nuovo Cimento,11, 401 (1973).