@article{DE_1970_6_12_a1,
     author = {A. A. Andronov and E. A. Leontovich},
     title = {Sufficient conditions for the {\textquotedblleft}structural instability of the first degree{\textquotedblright} of a dynamical system on the plane},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2121--2134},
     year = {1970},
     volume = {6},
     number = {12},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1970_6_12_a1/}
}