1. A. Bassetto, L. Lusanna andM. Toller:Nuovo Cimento,31 A, 375 (1976).
2. G. Ranft andJ. Ranft:Nucl. Phys.,69 B, 285 (1974);A. Di Giacomo: Scuola Normale Superiore di Pisa, preprint S.N.S. 18 (1975). Further references concerning fireball models are given in ref. (1).
3. A. Bassetto:Suppl. J. Physique,34, C 1 (1973).
4. A. Krzywicki andB. Petersson:Phys. Rev. D,6, 926 (1972).
5. J. Finkelstein andR. D. Peccèi:Phys. Rev. D,6, 2606 (1972).