@article{DE_1975_11_2_a23,
     author = {G. S. Rychkov},
     title = {The maximal number of limit cycles of the system $\dot{y}=-x$, $\dot{x}=y-\sum_{i=0}^2a_i x^{2i+1}$ is equal to two},
     journal = {Differencialʹnye uravneni\^a},
     pages = {390--391},
     publisher = {mathdoc},
     volume = {11},
     number = {2},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1975_11_2_a23/}
}