@article{DE_1999_35_1_a9,
     author = {N. A. Izobov and A. S. Platonov},
     title = {On the existence of a linear {Pfaffian} system with a disconnected lower characteristic set of positive measure},
     journal = {Differencialʹnye uravneni\^a},
     pages = {65--71},
     publisher = {mathdoc},
     volume = {35},
     number = {1},
     year = {1999},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1999_35_1_a9/}
}