@inproceedings{Per-Ali-Aly-Sch-1993,
    author={Jérôme Perez and J.-M. Alimi and Jean-Jacques Aly and H. 
           Scholl },
    title={Stability of spherical stellar systems by symplectic methods : 
           numerical test },
    booktitle={N Body gravitating systems },
    year={1993 },
    publisher={F. Combes and L. Athanassoula },
}