@article{DE_1971_7_6_a4,
     author = {N. A. Izobov},
     title = {A refinement of the estimate in the freezing method for a two-dimensional system with coincident characteristic numbers},
     journal = {Differencialʹnye uravneni\^a},
     pages = {990--996},
     publisher = {mathdoc},
     volume = {7},
     number = {6},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1971_7_6_a4/}
}