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Hasse diagrams with large chromatic number
Bulletin of the London Mathematical Society ( IF 0.9 ) Pub Date : 2021-01-15 , DOI: 10.1112/blms.12457
Andrew Suk 1 , István Tomon 2
Affiliation  

For every positive integer n , we construct a Hasse diagram with n vertices and independence number O ( n 3 / 4 ) . Such graphs have chromatic number Ω ( n 1 / 4 ) , which significantly improves the previously best-known constructions of Hasse diagrams having chromatic number Θ ( log n ) . In addition, if we also require girth of at least k 5 , we construct such Hasse diagrams with independence number at most n 1 1 2 k 4 + o ( 1 ) . The proofs are based on the existence of point-line arrangements in the plane with many incidences and avoids certain forbidden subconfigurations, which we find of independent interest.

中文翻译:

具有大色数的哈斯图

对于每个正整数 n ,我们构造了一个哈斯图 n 顶点和独立数 ( n 3 / 4 ) . 这样的图有色数 Ω ( n 1 / 4 ) ,这显着改进了先前最著名的具有色数的哈斯图的构造 Θ ( 日志 n ) . 此外,如果我们还要求周长至少为 5 ,我们最多构造这样的具有独立数的哈斯图 n 1 - 1 2 - 4 + ( 1 ) . 证明是基于平面中点线排列的存在性,并避免了某些我们认为具有独立意义的禁止子配置。
更新日期:2021-01-15
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