1. For a review on the classical Veneziano model seeV. Alessandrini, D. Amati, M. LeBellac andD. Olive:Phys. Rep. 1 C (1971). Other models are given byK. Bardakci andM. B. Halpern:Phys. Rev. D,3, 2493 (1971);L. Clavelli:Phys. Rev. D,3 3166 (1971);A. Neveu andJ. H. Schwarz:Nucl. Phys.,31 B, 86 (1972).
2. A. Neveu andJ. H. Schwarz:Nucl. Phys.,31 B, 86 (1972).
3. R. C. Brower:Phys. Rev. D,6, 1655 (1972).