Some general theorems are available about the existence and global continuation of periodic solutions in symmetric delay differential equations.

关于对称时滞微分方程中的周期解的存在性和全局持续存在性，现在已有一些一般性的理论。

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By using the continuation theorem of topology degree theory and properties of nonsingular M-matrix, we obtain sufficient conditions for the existence of positive periodic solutions of this system.

利用拓扑度理论中的连续定理以及M -矩阵的性质获得了该系统正周期解存在的充分条件。

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Sufficient conditions for the existence of positive periodic solutions are established by applying the continuation theorem of coincidence degree theory.

将应用叠合度理论的延拓定理建立正周期解存在的充分条件。

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Unfortunately, it appears he does not believe he can win with the two methods he would most likely prefer: continuation of a message of hope and optimism and proposals of realistic and even radical solutions to fix the economy.

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