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arXiv 1903.08056math.CO
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关于Kneser图的一般位置问题

On the general position problem on Kneser graphs

Balázs Patkós

摘要:

在图$G$中,两个顶点$x$和$y$之间的测地线是连接$x$和$y$的最短路径。如果$S$的顶点不位于$S$的两个其它顶点之间的任何测地线上,则$G$的顶点的子集$S$处于一般位置。一般位置上最大顶点集的大小是一般位置数,我们用$gp(G)$表示。最近,Ghorbani等人证明了对任何$k$,如果$n\ge k^3-k^2+2k-2$,则$gp(Kn_{n,k})=\binom{n-1}{k-1}$,其中$Kn_{n,k}$表示Kneser图.我们改进了他们的结果,并证明了同样的结论也适用于$n\ge 2.5k-0.5$,并且这个界是最好的可能界。我们的主要工具是交叉相交的家庭和Bollobás不等式相交集对系统的一个结果略有推广。

英文摘要:

In a graph $G$, a geodesic between two vertices $x$ and $y$ is a shortest path connecting $x$ to $y$. A subset $S$ of the vertices of $G$ is in general position if no vertex of $S$ lies on any geodesic between two other vertices of $S$. The size of a largest set of vertices in general position is the general position number that we denote by $gp(G)$. Recently, Ghorbani et al, proved that for any $k$ if $n\ge k^3-k^2+2k-2$, then $gp(Kn_{n,k})=\binom{n-1}{k-1}$, where $Kn_{n,k}$ denotes the Kneser graph. We improve on their result and show that the same conclusion holds for $n\ge 2.5k-0.5$ and this bound is best possible. Our main tools are a result on cross-intersecting families and a slight generalization of Bollobás's inequality on intersecting set pair systems.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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