@article{SM_1969_9_3_a1,
     author = {S. Kh. Aranson},
     title = {Trajectories on nonorientable two-dimensional manifolds},
     journal = {Sbornik. Mathematics},
     pages = {297--313},
     publisher = {mathdoc},
     volume = {9},
     number = {3},
     year = {1969},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1969_9_3_a1/}
}