@article{DE_1980_16_5_a5,
     author = {V. S. Vladimirov and V. V. Zharinov},
     title = {Closed forms associated with linear differential operators},
     journal = {Differencialʹnye uravneni\^a},
     pages = {845--867},
     publisher = {mathdoc},
     volume = {16},
     number = {5},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_5_a5/}
}