@article{IM_1994__117_1_144216,
     author = {Mark Pollicott and Richard Sharp},
     title = {Orbit counting for some discrete groups acting on simply connected manifolds with negative curvature.},
     journal = {Inventiones mathematicae},
     pages = {275--302},
     publisher = {mathdoc},
     volume = {117},
     number = {1},
     year = {1994},
     zbl = {0804.58009},
     url = {http://geodesic.mathdoc.fr/item/IM_1994__117_1_144216/}
}