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。
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.
获得了内积空间关于弱闭凸集的最佳逼近元的存在性及其刻划定理。
In the inner product space, the existence theory of best approximation element was obtained and described.
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。
It is obtained that a necessary and sufficient condition for a closed fuzzy set to be a convex fuzzy set.
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