English

Bispindles in strongly connected digraphs with large chromatic number

Combinatorics 2017-03-08 v1

Abstract

A (k1+k2)(k_1+k_2)-bispindle is the union of k1k_1 (x,y)(x,y)-dipaths and k2k_2 (y,x)(y,x)-dipaths, all these dipaths being pairwise internally disjoint. Recently, Cohen et al. showed that for every (1,1)(1,1)- bispindle BB, there exists an integer kk such that every strongly connected digraph with chromatic number greater than kk contains a subdivision of BB. We investigate generalisations of this result by first showing constructions of strongly connected digraphs with large chromatic number without any (3,0)(3,0)-bispindle or (2,2)(2,2)-bispindle. Then we show that strongly connected digraphs with large chromatic number contains a (2,1)(2,1)-bispindle, where at least one of the (x,y)(x,y)-dipaths and the (y,x)(y,x)-dipath are long.

Cite

@article{arxiv.1703.02230,
  title  = {Bispindles in strongly connected digraphs with large chromatic number},
  author = {N. Cohenn and F. Havet and W. Lochet and R. Lopes},
  journal= {arXiv preprint arXiv:1703.02230},
  year   = {2017}
}
R2 v1 2026-06-22T18:38:01.405Z