@article{DE_1997_33_12_a5,
     author = {N. A. Izobov},
     title = {On the existence of linear {Pfaffian} systems whose set of lower characteristic vectors has a positive plane measure},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1623--1630},
     publisher = {mathdoc},
     volume = {33},
     number = {12},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1997_33_12_a5/}
}