@article{RM_1995_50_4_a6,
     author = {B. S. Kruglikov},
     title = {On an invariant of the characteristic distribution},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {816--817},
     publisher = {mathdoc},
     volume = {50},
     number = {4},
     year = {1995},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1995_50_4_a6/}
}