@article{GDZPPN002100827, title = {A new curvature invariant and entropy of geodesic flow.}, journal = {Inventiones mathematicae}, volume = {75}, year = {1984}, pages = {455-462}, zbl = {0536.53048}, url = {http://dml.mathdoc.fr/item/GDZPPN002100827} }
Sarnak, P.; Osserman, R. A new curvature invariant and entropy of geodesic flow.. Inventiones mathematicae, Tome 75 (1984) pp. 455-462. http://gdmltest.u-ga.fr/item/GDZPPN002100827/