abstract convex set的用法和样例：
- Every weakly countably compact closed convex set in a locally convex space has the quasi-weak drop property.
- Projection onto convex sets (POCS) is used in this paper.
- The problem of the existence of a cone subdifferential for the cone convex set valued maps in the locally convex, linear and topological vector space is discussed.
- The existence and uniqueness of the element of best approximation on sequentially weak compact convex set in the normed linear spaces are studied,the conclusion of which improves and generalizes the existing result of Erwin kreysziy.
研究了在严格凸赋范线性空间上无穷维弱列紧凸子集的最佳近似元的存在与唯一性，所得结论改进和推广了Erwin Kreysziy 等已有的结果。