# Star chromatic index of cubic graphs

 Importance: Medium ✭✭
 Author(s): Dvorak, Zdenek Mohar, Bojan Samal, Robert
 Subject: Graph Theory
 Keywords: edge coloring star coloring
 Posted by: Robert Samal on: November 16th, 2010

The star chromatic index $\chi_s'(G)$ of a graph $G$ is the minimum number of colors needed to properly color the edges of the graph so that no path or cycle of length four is bi-colored.

\begin{question} Is it true that for every (sub)cubic graph $G$, we have $\chi_s'(G) \le 6$? \end{question}

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The \Def[star chromatic number]{Star coloring} is the more usual concept \cite{ACKKR,FRR}. Star chromatic index of a graph $G$ is simply the star chromatic number of the \Def{line graph} $L(G)$; the definition given above is easily seen to be equivalent.

Dvořák, Mohar, and Šámal \cite{DMS] show that every (sub)cubic graph $G$, satisfies $\chi_s'(G) \le 7$? On the other hand, it is simple to check that $\chi_s'(K_{3,3})=6$, so the conjecture, if true, is tight.

## Bibliography

[ACKKR] Albertson, Michael O.; Chappell, Glenn G.; Kierstead, Hal A.; Kündgen, André; Ramamurthi, Radhika: Coloring with no 2-Colored P4's, The Electronic Journal of Combinatorics 11 (1).

[FRR] Fertin, Guillaume; Raspaud, André; Reed, Bruce, Star coloring of graphs, Journal of Graph Theory 47 (3): 163-182, \doi{10.1002/jgt.20029} .

*[DMS] Dvořák, Zdeněk; Mohar, Bojan; Šámal, Robert: Star chromatic index, \arXiv{1011.3376}.

* indicates original appearance(s) of problem.