当适当有色图的色数的拓扑下界满足一定条件时,各种结果都保证了大的完全二部图的存在性。我们推广了三个这类定理,分别来自Simonyi和Tardos(Combinatorica,2006),Simonyi,Tardif和Zsbán(The Electronic Journal of Combinatorics,2013)和Chen(Journal of Combinatorial Theory,Series A,2011)。作为Chen定理的推广,我们得到了一类新的图族,它们的色数等于它们的圆色数,并且满足Hedetniemi关于圆色数的猜想.
英文摘要:
Various results ensure the existence of large complete bipartite graphs in properly colored graphs when some condition related to a topological lower bound on the chromatic number is satisfied. We generalize three theorems of this kind, respectively due to Simonyi and Tardos (Combinatorica, 2006), Simonyi, Tardif, and Zsbán (The Electronic Journal of Combinatorics, 2013), and Chen (Journal of Combinatorial Theory, Series A, 2011). As a consequence of the generalization of Chen's theorem, we get new families of graphs whose chromatic number equals their circular chromatic number and that satisfy Hedetniemi's conjecture for the circular chromatic number.
在满足某些特殊拓扑正则性条件的真有色图中,有几个拓扑结果保证了大的完全二部子图的存在。鉴于$\mathbb{Z}_p$引理,Alishahi和Hajiabolhassan [{ \it On the chromatic number of general Kneser hypergraphs,Journal of Combinatorial Theory,Series B,2015}]引入了Kneser hypergraphs ${\rm KG}^r({\mathcal H})$的色数的下界。接下来,Meunier [{ \it Colorful subhypergraphs in Kneser hypergraphs,The Electronic Journal of Combinatorics,2014}]通过证明任何适当着色的一般Kneser超图${\rm KG}^r({\mathcal H})$包含一个大的彩色$r$ -部子超图,只要$r$是素数,改进了他们的结果。本文给出了$\mathbb{Z}_p$ -Tucker引理的一些新的推广.从而在某些方面改进了Meunier的结果。给出了一致超图的色数和局部色数的一些新的下界。
On colorful generalizations of the Goodman--Pollack transversal problem
Center for Systems Biology Dresden(德累斯顿系统生物学中心);Technische Universität Dresden(德累斯顿工业大学);Max Planck Institute of Molecular Cell Biology and Genetics(马克斯·普朗克分子细胞生物学与遗传学研究所)
Cone and constrained colorful Carathéodory Theorems
Freie Universität Berlin(柏林自由大学);Mat. Institut SANU(塞尔维亚科学与艺术学院数学研究所);Institute for Information Transmission Problems RAS(俄罗斯科学院信息传输问题研究所);Moscow Institute of Physics and Technology(莫斯科物理技术学院)