@article{DE_2000_36_11_a21,
     author = {L. V. Detchenya and A. P. Sadovskii},
     title = {Letter to the editors: {{\textquotedblleft}Orbital} normal forms of two-dimensional analytic systems with zero linear and nonzero quadratic parts{\textquotedblright} {[Differ.} {Uravn.} 35 (1999), no. 1, 51{\textendash}57, 141; {MR1723202]}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1580},
     year = {2000},
     volume = {36},
     number = {11},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2000_36_11_a21/}
}