arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1609.05484math.COmath.ACmath.AG
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点、线、面等的Enumeration

Enumeration of points, lines, planes, etc

June Huh, Botong Wang

摘要:

在计数组合几何中最早的结果之一是德布鲁因和埃尔德什的下列定理:射影平面中的每一组点$E$至少确定$|E|$线,除非所有的点都包含在一条线中。Motzkin和其他人将结果扩展到更高的维度,他们表明,射影空间中的每一组点$E$至少确定$|E|$超平面,除非所有的点都包含在一个超平面中。设$E$是$d$维向量空间的生成子集。我们表明,在偏序集的子空间所跨越的$E$的子集,至少有尽可能多的$(d-k)$维的子空间,因为有$k$维的子空间,对于每个$k$最多$d/2$。这证实了道林和威尔逊的“头重脚轻”猜想的所有拟阵可实现的一些领域。证明依赖于$\ell$ -adic交集复形的分解定理包。

英文摘要:

One of the earliest results in enumerative combinatorial geometry is the following theorem of de Bruijn and Erdős: Every set of points $E$ in a projective plane determines at least $|E|$ lines, unless all the points are contained in a line. Motzkin and others extended the result to higher dimensions, who showed that every set of points $E$ in a projective space determines at least $|E|$ hyperplanes, unless all the points are contained in a hyperplane. Let $E$ be a spanning subset of a $d$-dimensional vector space. We show that, in the partially ordered set of subspaces spanned by subsets of $E$, there are at least as many $(d-k)$-dimensional subspaces as there are $k$-dimensional subspaces, for every $k$ at most $d/2$. This confirms the "top-heavy" conjecture of Dowling and Wilson for all matroids realizable over some field. The proof relies on the decomposition theorem package for $\ell$-adic intersection complexes.

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