@article{DE_2003_39_8_a1,
     author = {V. V. Basov and A. V. Skitovich},
     title = {A {Generalized} {Normal} {Form} and {Formal} {Equivalence} of {Two-Dimensional} {Systems} with {Quadratic} {Zero} {Approximation:} {I}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1016--1029},
     publisher = {mathdoc},
     volume = {39},
     number = {8},
     year = {2003},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2003_39_8_a1/}
}