@article{MAN_1939__116_160001,
     author = {J. Lense},
     title = {\"Uber isotrope {Mannigfaltigkeiten}},
     journal = {Mathematische Annalen},
     pages = {297--309},
     publisher = {mathdoc},
     volume = {116},
     year = {1939},
     zbl = {65.0757.01},
     url = {http://geodesic.mathdoc.fr/item/MAN_1939__116_160001/}
}