@article{MZM_1981_29_6_a15,
     author = {A. N. Varchenko},
     title = {Obstructions to local equivalence of distributions},
     journal = {Matemati\v{c}eskie zametki},
     pages = {939--947},
     year = {1981},
     volume = {29},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1981_29_6_a15/}
}