English

Chromatic-choosability of hypergraphs with high chromatic number

Combinatorics 2018-07-24 v1

Abstract

It was conjectured by Ohba and confirmed recently by Noel et al. that, for any graph GG, if V(G)2χ(G)+1|V(G)|\le 2\chi(G)+1 then χl(G)=χ(G)\chi_l(G)=\chi(G). This indicates that the graphs with high chromatic number are chromatic-choosable. We show that this is also the case for uniform hypergraphs and further propose a generalized version of Ohba's conjecture: for any rr-uniform hypergraph HH with r2r\geq 2, if V(H)rχ(H)+r1|V(H)|\le r\chi(H)+r-1 then χl(H)=χ(H)\chi_l(H)=\chi(H). We show that the condition of the proposed conjecture is sharp by giving two classes of rr-uniform hypergraphs HH with V(H)=rχ(H)+r|V(H)|= r\chi(H)+r and χl(H)>χ(H)\chi_l(H)>\chi(H). To support the conjecture, we give two classes of rr-uniform hypergraphs HH with V(H)=rχ(H)+r1|V(H)|= r\chi(H)+r-1 and prove that χl(H)=χ(H)\chi_l(H)=\chi(H).

Keywords

Cite

@article{arxiv.1807.08273,
  title  = {Chromatic-choosability of hypergraphs with high chromatic number},
  author = {Wei Wang and Jianguo Qian},
  journal= {arXiv preprint arXiv:1807.08273},
  year   = {2018}
}

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18 pages