English

The competition-common enemy graphs of digraphs satisfying Conditions $C(p)$ and $C'(p)$

Combinatorics 2011-02-18 v2

Abstract

S. -R. Kim and F. S. Roberts (2002) introduced the following conditions C(p)C(p) and C(p)C'(p) for digraphs as generalizations of the condition for digraphs to be semiorders. The condition C(p)C(p) (resp. C(p)C'(p)) is: For any set SS of pp vertices in DD, there exists xSx \in S such that ND+(x)ND+(y)N^+_D(x) \subseteq N^+_D(y) (resp. ND(x)ND(y)N^-_D(x) \subseteq N^-_D(y)) for all ySy \in S, where ND+(x)N^+_D(x) (resp. ND(x)N^-_D(x)) is the set of out-neighbors (resp. in-neighbors) of xx in DD. The competition graph of a digraph DD is the (simple undirected) graph which has the same vertex set as DD and has an edge between two distinct vertices xx and yy if ND+(x)ND+(y)N^+_D(x) \cap N^+_D(y) \neq \emptyset. Kim and Roberts characterized the competition graphs of digraphs which satisfy Condition C(p)C(p). The competition-common enemy graph of a digraph DD is the graph which has the same vertex set as DD and has an edge between two distinct vertices xx and yy if it holds that both ND+(x)ND+(y)N^+_D(x) \cap N^+_D(y) \neq \emptyset and ND(x)ND(y)N^-_D(x) \cap N^-_D(y) \neq \emptyset. In this note, we characterize the competition-common enemy graphs of digraphs satisfying Conditions C(p)C(p) and C(p)C'(p).

Keywords

Cite

@article{arxiv.1006.2631,
  title  = {The competition-common enemy graphs of digraphs satisfying Conditions $C(p)$ and $C'(p)$},
  author = {Yoshio Sano},
  journal= {arXiv preprint arXiv:1006.2631},
  year   = {2011}
}

Comments

8 pages, 2 figures