English

Connected equitably $\Delta$-colorable realizations with $k$-factors

Combinatorics 2025-03-04 v1

Abstract

A graph GG is said to be equitably cc-colorable if its vertices can be partitioned into cc independent sets that pairwise differ in size by at most one. Chen, Lih, and Wu conjectured that every connected graph GG with maximum degree Δ(G)2\Delta(G)\geq 2 has an equitable coloring with Δ(G)\Delta(G) colors, except when GG is complete, an odd cycle, or a balanced bipartite graph with odd sized partitions. Suppose GG is a connected graph with a kk-factor (a regular spanning subgraph) FF such that GG is not complete, a 11-factor, nor an odd cycle. When k1k\geq 1 we demonstrate that there is a connected (k1)(k-1) edge-connected equitably Δ(G)\Delta(G)-colorable graph HH with a kk-factor FF' such that GE(F)=HE(F)G-E(F)=H-E(F'). If we drop the requirement that GE(F)=HE(F)G-E(F)=H-E(F'), then we can say more. Considering the non-increasing degree sequence π=(d1,,dn)\pi=(d_{1},\ldots, d_{n}) of GG where di=degG(vi)d_{i}=deg_{G}(v_{i}) for all vertices {v1,,vn}\{v_{1},\ldots,v_{n}\} of GG, we call m(π)=max{idii}m(\pi)=\max\{i|d_{i}\geq i\} the strong index of π\pi. For k0k\geq 0, we can show that for every cmaxlm(π){dl+l2}+1c\geq \max_{l\leq m(\pi)}\bigg\{\bigg\lfloor\frac{d_{l}+l}{2}\bigg\rfloor\bigg\}+1 we can find a connected (k1)(k-1) edge-connected equitably cc-colorable realization HH of π\pi that has a kk-factor. In a third theorem we show that if dd1dn+1d1dn+k1d_{d_{1}-d_{n}+1}\geq d_{1}-d_{n}+k-1, then some realization of π\pi has a kk-factor. Together, these three theorems allow us to prove that for all kk, there is a connected equitably Δ(G)\Delta(G)-colorable realization HH of π\pi with a kk-factor. Thus, giving support to the validity of the Chen-Lih-Wu Conjecture.

Keywords

Cite

@article{arxiv.2503.00222,
  title  = {Connected equitably $\Delta$-colorable realizations with $k$-factors},
  author = {James M. Shook},
  journal= {arXiv preprint arXiv:2503.00222},
  year   = {2025}
}
R2 v1 2026-06-28T22:02:39.530Z