%0 Journal Article %A A. A. Andronov %A E. A. Leontovich %T Sufficient conditions for the “structural instability of the first degree” of a dynamical system on the plane %J Differencialʹnye uravneniâ %D 1970 %P 2121-2134 %V 6 %N 12 %U http://geodesic.mathdoc.fr/item/DE_1970_6_12_a1/ %G ru %F DE_1970_6_12_a1