@article{MZM_1990_48_1_a4,
     author = {A. M. Vinogradov and V. A. Yumaguzhin},
     title = {Differential invariants of webs on 2-dimensional manifolds},
     journal = {Matemati\v{c}eskie zametki},
     pages = {26--37},
     publisher = {mathdoc},
     volume = {48},
     number = {1},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1990_48_1_a4/}
}