Enhancing the Erd\H{o}s-Lov\'asz Tihany Conjecture for line graphs of multigraphs

Abstract

In this paper, we prove an enhanced version of the Erd\H{o}s-Lov\'asz Tihany Conjecture for line graphs of multigraphs. That is, for every graph $G$ whose chromatic number $\chi(G)$ is more than its clique number $\omega(G)$ and for nonnegative integer $\ell$, any two integers $s,t \geq 3.5\ell+2$ with $s+t = \chi(G)+1$, there is a partition $(S,T)$ of the vertex set $V(G)$ such that $\chi(G[S])\geq s$ and $\chi(G[T])\geq t+\ell$. In particular, when $\ell=1$, we can obtain the same result just for any $s,t\geq4$. The Erd\H{o}s-Lov\'asz Tihany conjecture is a special case when $\ell=0$.