@article{DE_1973_9_6_a20,
     author = {A. V. Osipov},
     title = {On the question of the existence of a transformation to normal form},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1149--1150},
     publisher = {mathdoc},
     volume = {9},
     number = {6},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1973_9_6_a20/}
}