@article{DE_1985_21_9_a5,
     author = {A. P. Sadovskii},
     title = {Formal orbital normal forms of two-dimensional systems with nonzero linear part},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1509--1516},
     publisher = {mathdoc},
     volume = {21},
     number = {9},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1985_21_9_a5/}
}