对于二元函数的二重极限，重点是极限的存在性及其求解方法。

For double limit of a binary function, the existence of the limit and the methods to seek its solution are emphasis among our focus.

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本文阐明二重极限与二次极限的不确定关系，给出齐次函数的极限不存在的判定方法。

The uncertain relationship between the double limit and the quadratic limit is explained and the determination methods to the nonexistence of the odd function's limit are given.

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给出了完整的分支图和各区域上的相轨线结构。结果表明，非对称项引起二重极限环分支和分支曲线的复杂性。

Moreover, a formula for calculating double limit cycle bifurcation is derived. Finally, the complete bifurcation diagrams and phase portraits are obtained.

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