Positions of limit-cycles of the system $\frac{dx}{dt}=\sum_{0\le{i+k}\le2}a_{ik}x^iy^k$, $\frac{dy}{dt}=\sum_{0\le{i+k}\le2}b_{ik}x^iy^k$

Tung Chin-chu

 English version: , 1959, 8:2, 151–171

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