@article{SM_1969_7_3_a4,
     author = {Yu. S. Ilyashenko},
     title = {The origin of limit cycles under perturbation of the equation $\dfrac{dw}{dz}=-\dfrac{R_z}{R_w}$, where $R(z,w)$ is a~polynomial},
     journal = {Sbornik. Mathematics},
     pages = {353--364},
     publisher = {mathdoc},
     volume = {7},
     number = {3},
     year = {1969},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1969_7_3_a4/}
}