@article{MZM_1994_55_5_a0,
     author = {V. K. Beloshapka},
     title = {Geometric invariants of a $CR$-manifold},
     journal = {Matemati\v{c}eskie zametki},
     pages = {3--12},
     year = {1994},
     volume = {55},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1994_55_5_a0/}
}