1. I. T. Todorov, M. C. Mintchev andV. B. Petkova:Conformal Invariance in Quantum Field Theory, inQuaderni della Scuola Normale Superiore (Pisa, 1978).
2. M. C. Prati:Nuovo Cimento A,68, 11 (1982).
3. L. Bonora, G. Sartori andM. Tonin:Nuovo Cimento A,10, 667 (1972).
4. S. Ferrara, R. Gatto andA. F. Grillo:Conformal Algebra in Space-time and Operator Product Expansion, Springer Tracts in Modern Physics, Vol.67 (Berlin, 1973).
5. S. Ferrara, R. Gatto, A. F. Grillo andG. Parisi:General consequences of conformal algebra, inScale and Conformal Symmetry, edited byR. Gatto (New York, N. Y., 1973).