1. L. Van Hove:Mem. Acad. Roy. Belg.,26, (1951);
2. Bull. Cl. Sci. Acad. Roy. Belg.,37 610 (1951);
3. V. Uhlhorn:Ark Fys.,11, 87 (1956);
4. K. B. Wolf:Group Theory and its Applications, Vol.3, edited byE. M. Loebl (New York, N. Y., 1971);R. Abraham:Foundations of Mechanics (New York, N. Y., 1967).
5. J. M. Souriau:Comm. Math. Phys.,1, 374 (1966);R. F. Streater:Comm. Math. Phys.,2, 354 (1966);E. Onofri andM. Pauri:Journ. Math. Phys.,13, 533 (1972).