@article{MAT_1962_6_2_a4,
     author = {Tung Chin-chu},
     title = {Positions of limit-cycles of the system $\frac{dx}{dt}=\sum_{0\le{i+k}\le2}a_{ik}x^iy^k$, $\frac{dy}{dt}=\sum_{0\le{i+k}\le2}b_{ik}x^iy^k$},
     journal = {Matematika},
     pages = {150--168},
     publisher = {mathdoc},
     volume = {6},
     number = {2},
     year = {1962},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MAT_1962_6_2_a4/}
}