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A collection of sets has the -property if out of every elements of there are that have a point in common. A transversal of a collection of sets is a set that intersects every member of . Gr"unbaum conjectured that every family of closed, convex sets in the plane with the -property and at least two elements that are compact has a transversal of bounded cardinality. Here we construct a counterexample to his conjecture. On the positive side, we also show that if such a collection contains two {\em disjoint} compacta then there is a transveral of cardinality at most 13.

生成讲解博客的中文版本

生成AI智能校验的中文版本