关于半单调集和单调映射的Helly型定理
A Helly-type theorem for semi-monotone sets and monotone maps
摘要：
我们考虑定义在实数上的O-极小结构上的集合和映射，例如实半代数或次解析集合。一个{ \em单调映射}是通常的一元单调函数的多维推广，而单调映射的图的闭包是紧凸集的推广.在一个常数相同的函数的特殊情况下，这样的图被称为{ \em半单调集}。单调映射的图通常是非凸的，它们的交集与凸集的交集不同，可以是拓扑复杂的。特别地，这样的交集不一定是单调映射的图。然而，我们证明了一个Helly型定理，即对于$\Real^n$的子集的有限族，如果基数至多为$n+1$的子族的所有交集都是非空的且是单调映射的图，则整个族的交集都是非空的且是单调映射的图。
英文摘要：
We consider sets and maps defined over an o-minimal structure over the reals, such as real semi-algebraic or subanalytic sets. A {\em monotone map} is a multi-dimensional generalization of a usual univariate monotone function, while the closure of the graph of a monotone map is a generalization of a compact convex set. In a particular case of an identically constant function, such a graph is called a {\em semi-monotone set}. Graphs of monotone maps are, generally, non-convex, and their intersections, unlike intersections of convex sets, can be topologically complicated. In particular, such an intersection is not necessarily the graph of a monotone map. Nevertheless, we prove a Helly-type theorem, which says that for a finite family of subsets of $\Real^n$, if all intersections of subfamilies, with cardinalities at most $n+1$, are non-empty and graphs of monotone maps, then the intersection of the whole family is non-empty and the graph of a monotone map.
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