@article{DE_1971_7_2_a26,
     author = {B. S. Kalitin},
     title = {Letter to the editor},
     journal = {Differencialʹnye uravneni\^a},
     pages = {378},
     publisher = {mathdoc},
     volume = {7},
     number = {2},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1971_7_2_a26/}
}