@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/}
}