1. E. Berger: rapporteur's talk at theInternational Colloquium on Multiparticle Dynamics. May 25–28, 1971.
2. G. Giacomelli: paper presented at theVII Rencontre de Moriond sur les Interactions Electromagnetiques, March 1972.
3. W. Kittel: lecture given at theScandinavian Conference on High-Energy Physics, Spatind, January 1972, CERN preprint D.Ph.II/PHYS. 72-II.
4. R. Hagedorn:Nuovo Cimento,56 A, 1027 (1968);R. Hagedorn andJ. Ranft:Nucl. Phys.,48 B, 157 (1972).
5. E. Yen andE. L. Berger:Phys. Rev. Lett.,24, 695 (1970).