Graphs with girth $2\ell+1$ and without longer odd holes that contain an odd $K_4$-subdivision

TL;DR

This paper investigates the structure of certain graphs with specific girth and odd hole constraints, proving they are 3-colorable and that certain critical graphs cannot contain odd $K_4$-subdivisions, advancing understanding of graph coloring.

Contribution

It proves that no 4-vertex-critical graph in the union of classes with girth at least 11 contains an odd $K_4$-subdivision, leading to a proof of 3-colorability for these classes.

Findings

No 4-vertex-critical graphs in the union have odd $K_4$-subdivisions.

All graphs in the union are 3-colorable.

Progress on Wu, Xu, and Xu's conjecture for graphs with larger girth.

Abstract

We say that a graph $G$ has an {\em odd $K_4$-subdivision} if some subgraph of $G$ is isomorphic to a $K_4$-subdivision and whose faces are all odd holes of $G$. For a number $\ell\geq 2$, let $\mathcal{G}_{\ell}$ denote the family of graphs which have girth $2\ell+1$ and have no odd hole with length greater than $2\ell+1$. Wu, Xu and Xu conjectured that every graph in $\bigcup_{\ell\geq2}\mathcal{G}_{\ell}$ is 3-colorable. Recently, Chudnovsky et al. and Wu et al., respectively, proved that every graph in $\mathcal{G}_2$ and $\mathcal{G}_3$ is 3-colorable. In this paper, we prove that no $4$-vertex-critical graph in $\bigcup_{\ell\geq5}\mathcal{G}_{\ell}$ has an odd $K_4$-subdivision. Using this result, Chen proved that all graphs in $\bigcup_{\ell\geq5}\mathcal{G}_{\ell}$ are 3-colorable.