@article{CRMATH_2005__341_9_567_0,
     author = {G\'erard Besson and Gilles Courtois and Sylvestre Gallot},
     title = {Growth of discrete groups of isometries in negative curvature: a gap-property},
     journal = {Comptes Rendus. Math\'ematique},
     pages = {567--572},
     publisher = {Elsevier},
     volume = {341},
     number = {9},
     year = {2005},
     doi = {10.1016/j.crma.2005.09.025},
     language = {en},
}