English

Brooks' theorem with forbidden colors

Combinatorics 2023-03-14 v1

Abstract

We consider extensions of Brooks' classic theorem on vertex coloring where some colors cannot be used on certain vertices. In particular we prove that if GG is a connected graph with maximum degree Δ(G)4\Delta(G) \geq 4 that is not a complete graph and PV(G)P \subseteq V(G) is a set of vertices where either (i) at most Δ(G)2\Delta(G)-2 colors are forbidden for every vertex in PP, and any two vertices of PP are at distance at least 44, or (ii) at most Δ(G)3\Delta(G)-3 colors are forbidden for every vertex in PP, and any two vertices of PP are at distance at least 33, then there is a proper Δ(G)\Delta(G)-coloring of GG respecting these constraints. In fact, we shall prove that these results hold in the more general setting of list colorings. These results are sharp.

Keywords

Cite

@article{arxiv.2303.06917,
  title  = {Brooks' theorem with forbidden colors},
  author = {Carl Johan Casselgren},
  journal= {arXiv preprint arXiv:2303.06917},
  year   = {2023}
}
R2 v1 2026-06-28T09:13:34.643Z