@article{DE_1980_16_1_a13,
     author = {S. G. Pyatkov},
     title = {An equation of composite type},
     journal = {Differencialʹnye uravneni\^a},
     pages = {117--123},
     publisher = {mathdoc},
     volume = {16},
     number = {1},
     year = {1980},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1980_16_1_a13/}
}