@article{DE_1972_8_4_a8,
     author = {N. A. Zhikhar},
     title = {Certain properties of differential operators with variable coefficients that depend on the form of the domain},
     journal = {Differencialʹnye uravneni\^a},
     pages = {645--651},
     publisher = {mathdoc},
     volume = {8},
     number = {4},
     year = {1972},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1972_8_4_a8/}
}