The scheme number three is: a connection rod (12) is hinged between the lower lever (5) and the upper lever (7).

方案三是：下杠杆(5)与上杠杆(7)之间铰接有连杆(12)。

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The model of bilevel linear programming which upper lever has without constraint is discussed in this paper, the algorithm which can find all vertexes of the programming is given.

讨论的是上层不带约束的二层线性规划模型，给出了求其所有顶点的算法，此算法为进行二层线性规划的灵敏度分析打下了坚实的基础。

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Safety and easy operation: hidden air leaking hole for opening fixture cover easily while pulling up hand lever of the upper cover.

操作方便，安全：隐藏式泄气孔，拉起上盖把手即可打开治具，操作简易，安全性高。

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