English

The typical structure of oriented graphs and digraphs with forbidden blow-up of transitive tournaments

Combinatorics 2026-05-26 v2 Optimization and Control

Abstract

For integers r2r\ge 2, t1t\ge 1 and a real number a(3/2,2]a\in(3/2,2], we study the typical structure of oriented graphs and digraphs that do not contain a blow-up Tr+1tT_{r+1}^t of a transitive tournament. We prove that almost every Tr+1tT_{r+1}^t-free oriented graph on n vertices admits an r-partition V1VrV_1\cup\cdots\cup V_r such that each induced subgraph G[Vi]G[V_i] is T2tT_2^t-free, and the same holds for almost every Tr+1tT_{r+1}^t-free digraph.Consequently, the number f(n,Tr+1t)f(n,T_{r+1}^t) of labelled Tr+1tT_{r+1}^t-free oriented graphs satisfies f(n,Tr+1t)=Pn,r,t(1+o(1))f(n,T_{r+1}^t)=|\mathcal{P}_{n,r,t}|(1+o(1)), where Pn,r,t\mathcal{P}_{n,r,t} is the family of oriented graphs admitting such an r-partition with each part T2tT_2^t-free; an analogous statement holds for digraphs.When t=1t=1 this recovers the result of K"uhn, Osthus, Townsend and Zhao (2017) that almost all Tr+1T_{r+1}-free oriented graphs (resp. digraphs) are r-partite, thereby confirming a generalised form of Cherlin's conjecture. Our proof combines the hypergraph container method, a weighted Erd\H{o}s-Stone theorem, and a stability analysis for near-extremal Tr+1tT_{r+1}^t-free digraphs.

Keywords

Cite

@article{arxiv.2605.18458,
  title  = {The typical structure of oriented graphs and digraphs with forbidden blow-up of transitive tournaments},
  author = {Meili Liang and Yue Guan and Ruiling Zheng and Jianxi Liu},
  journal= {arXiv preprint arXiv:2605.18458},
  year   = {2026}
}