English

Directed graphs without rainbow triangles

Combinatorics 2023-08-08 v2

Abstract

One of the most fundamental results in graph theory is Mantel's theorem which determines the maximum number of edges in a triangle-free graph of order nn. Recently a colorful variant of this problem has been solved. In such a variant we consider cc graphs on a common vertex set, thinking of each graph as edges in a distinct color, and want to determine the smallest number of edges in each color which guarantees existence of a rainbow triangle. Here, we solve the analogous problem for directed graphs without rainbow triangles, either directed or transitive, for any number of colors. The constructions and proofs essentially differ for c=3c=3 and c4c \geq 4 and the type of the forbidden triangle. Additionally, we also solve the analogous problem in the setting of oriented graphs.

Keywords

Cite

@article{arxiv.2308.01461,
  title  = {Directed graphs without rainbow triangles},
  author = {Sebastian Babiński and Andrzej Grzesik and Magdalena Prorok},
  journal= {arXiv preprint arXiv:2308.01461},
  year   = {2023}
}

Comments

20 pages

R2 v1 2026-06-28T11:46:53.531Z