1. An extensive list of references on cluster models can be found in:A. Białas:Correlations in particle production at high energies, inProceedings IV Symposium on Multiparticle Hadrodynamics (Pavia, 1973), p. 93;J. Ranft:Correlations in multiparticle production, inProceedings of the Leipzig V International Symposium on Many-Particle Hadrodynamics (Eisenach and Leipzig, G.D.R., 1974);L. Foà:Phys. Rep.,22 C, 1 (1975).
2. T. Del Prete:Riv. Nuovo Cimento,5, 532 (1975);S. R. Amendolia, G. Bellettini, L. Bosisio, P. L. Braccini, C. Bradaschia, R. Castaldi, V. Cavasinni, T. Del Prete, L. Foà, P. Giromini, P. Laurelli, A. Menzione, L. Ristori, G. Sanguinetti, M. Valdata, G. Finocchiaro, P. Grannis, D. Green, H. Jostlein, R. Kephart andR. Thun:Nuovo Cimento,31 A, 17 (1976);P. Darriulat: talk at theVI International Colloquium on Multiparticle Reactions (Oxford, 1975).
3. Z. Koba, H. B. Nielsen andP. Olesen:Nucl. Phys.,43 B, 175 (1972).
4. U. Amaldi, R. Biancastelli, C. Bosio, G. Matthiae, J. V. Allaby, W. Bartel, G. Cocconi, A. N. Diddens, R. W. Dobinson andA. M. Wetherell:Phys. Lett. B,44, 112 (1973);S. R. Amendolia, G. Bellettini, P. L. Braccini, C. Bradaschia, R. Castaldi, V. Cavasinni, C. Cerri, T. Del Prete, L. Foà, P. Giromini, P. Laurelli, A. Menzione, L. Ristori, G. Sanguinetti, M. Valdata, G. Finocchiaro, P. Grannis, D. Green, R. Mustard andR. Thun:Phys. Lett.,44 B, 119 (1973).
5. M. Anselmino andA. Ballestrero:Lett. Nuovo Cimento,15, 329 (1976).