We examine subgraphs of oriented graphs in the context of oriented coloring that are analogous to cliques in traditional vertex coloring. Bounds on the sizes of these subgraphs are given for planar, outerplanar, and series-parallel graphs. In particular, the main result of the paper is that a planar graph cannot contain an induced subgraph D with more than 36 vertices such that each pair of vertices in D are joined by a directed path of length at most two.
@article{bwmeta1.element.bwnjournal-article-doi-10_7151_dmgt_1237, author = {William F. Klostermeyer and Gary MacGillivray}, title = {Analogues of cliques for oriented coloring}, journal = {Discussiones Mathematicae Graph Theory}, volume = {24}, year = {2004}, pages = {373-387}, zbl = {1063.05044}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_7151_dmgt_1237} }
William F. Klostermeyer; Gary MacGillivray. Analogues of cliques for oriented coloring. Discussiones Mathematicae Graph Theory, Tome 24 (2004) pp. 373-387. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_7151_dmgt_1237/
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