1. E Grgin and A Petersen,J. Math. Phys. 15, 764 (1974)
2. J Moyal,Proc. Cambridge Philos. Soc. 45 99 (1949)
3. H D Doebner and J D Hennig (eds),Quantum groups proceedings, Clausthal, FRG 1989, Lecture notes in physics, (Springer-Verlag, Berlin, 1990)370
4. T Curtright, D Fairlie and C Zachos (eds),Quantum groups: Proceedings of Argonne workshop (World Scientific, Singapore, 1991)
5. A Connes,Geometrie non-commutative (Inter Editions 1990)