@article{IVM_1975_7_a9,
     author = {Ya. L. Shapiro and S. E. Landa},
     title = {Direction fields on~2-manifolds},
     journal = {Izvesti\^a vys\v{s}ih u\v{c}ebnyh zavedenij. Matematika},
     pages = {80--91},
     year = {1975},
     number = {7},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/IVM_1975_7_a9/}
}