1. G. Veneziano:Nuovo Cimento,57 A, 190 (1968).
2. S. Humble:Lett. Nuovo Cimento,2, 541 (1969).
3. K. Bardakci andH. Ruegg:Phys. Lett.,28 B, 306 (1968);Chan Hong-Mo:Phys. Lett.,28 B, 425 (1969);M. Virasoro:Phys. Rev. Lett.,22, 37 (1969);Chan Hong-Mo andTsou Sheung-Tsun:Phys. Lett.,28 B, 485 (1969).
4. J. G. Cordes:Phys. Rev.,156, 1707 (1967).
5. T b depends onS b ,S c etc. so the convention of Sect.2 is to be applied.