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@article{MAN_1995__301_4_165314, author = {Ursula Hammenst\"adt}, title = {Invariant two-forms for geodesic flows.}, journal = {Mathematische Annalen}, pages = {677--698}, publisher = {mathdoc}, volume = {301}, number = {4}, year = {1995}, zbl = {0821.58033}, url = {http://geodesic.mathdoc.fr/item/MAN_1995__301_4_165314/} }
Ursula Hammenstädt. Invariant two-forms for geodesic flows.. Mathematische Annalen, Tome 301 (1995) no. 4, pp. 677-698. http://geodesic.mathdoc.fr/item/MAN_1995__301_4_165314/