The core is a set which satisfies a system of weak linear inequalities, so it is closed and convex.

中心是一个满足弱线性不等式的合集，因此它是封闭的、凸的。

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Based on geometry and convex set methods, this paper gives systemically the definitions of global and local convexity for planar closed parametric curve, and proves the two definitions are equivalent.

从几何和凸集的角度，系统地给出了平面闭参数曲线全局凸和局部凸定义，并且证明了这两个定义是等价的。

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It is obtained that a necessary and sufficient condition for a closed fuzzy set to be a convex fuzzy set.

引入线性拓扑空间中的凸闭模糊集概念，得到闭模糊集是凸模糊集的充分必要条件。

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