In this paper we study the chromatic number of graphs with two prescribed induced cycle lengths. It is due to Sumner that triangle-free and P₅-free or triangle-free, P₆-free and C₆-free graphs are 3-colourable. A canonical extension of these graph classes is , the class of all graphs whose induced cycle lengths are 4 or 5. Our main result states that all graphs of are 3-colourable. Moreover, we present polynomial time algorithms to 3-colour all triangle-free graphs G of this kind, i.e., we have polynomial time algorithms to 3-colour every with n₁,n₂ ≥ 4 (see Table 1). Furthermore, we consider the related problem of finding a χ-binding function for the class . Here we obtain the surprising result that there exists no linear χ-binding function for .
@article{bwmeta1.element.bwnjournal-article-doi-10_7151_dmgt_1149, author = {Bert Randerath and Ingo Schiermeyer}, title = {Colouring graphs with prescribed induced cycle lengths}, journal = {Discussiones Mathematicae Graph Theory}, volume = {21}, year = {2001}, pages = {267-281}, zbl = {1002.05026}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_7151_dmgt_1149} }
Bert Randerath; Ingo Schiermeyer. Colouring graphs with prescribed induced cycle lengths. Discussiones Mathematicae Graph Theory, Tome 21 (2001) pp. 267-281. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_7151_dmgt_1149/
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