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Acyclic edge-colouring
![$ \Delta $](/files/tex/e3f8e135c571143e94f1d4f236326b862080b200.png)
![$ (\Delta+2) $](/files/tex/6a77f06e08e0a0d164f09aa262634fe605297c08.png)
An edge-colouring with the property that every cycle contains edges of at least three distinct colours is called an acyclic edge-colouring. It is known (see [AMR]) that every graph of maximum degree has an acyclic edge-colouring of size
. The best upper bound so far is
and is due to Esperet and Parreau [EP]. It is also known (see [ASZ]) that this conjecture is true for graphs with girth at least
(for some fixed constant
).
Bibliography
[AMR] N. Alon, C. McDiarmid and B. Reed, Acyclic colouring of graphs, Random Structures and Algorithms 2 (1991), 277-288. MathSciNet
[ASZ] N. Alon, B. Sudakov and A. Zaks, Acyclic edge-colorings of graphs, J. Graph Theory 37 (2001), 157-167. MathSciNet
[EP] L. Esperet and A. Parreau, Acyclic edge-coloring using entropy compression, arXiv:1206.1535 [math.CO].
* indicates original appearance(s) of problem.