English

A note on extremal constructions for the Erd\H{o}s--Rademacher problem

Combinatorics 2024-10-08 v2

Abstract

For given positive integers r3r\ge 3, nn and e(n2)e\le \binom{n}{2}, the famous Erd\H os--Rademacher problem asks for the minimum number of rr-cliques in a graph with nn vertices and ee edges. A conjecture of Lov\'asz and Simonovits from the 1970s states that, for every r3r\ge 3, if nn is sufficiently large then, for every e(n2)e\le \binom{n}{2}, at least one extremal graph can be obtained from a complete partite graph by adding a triangle-free graph into one part. In this note, we explicitly write the minimum number of rr-cliques predicted by the above conjecture. Also, we describe what we believe to be the set of extremal graphs for any r4r\ge 4 and all large~nn, amending the previous conjecture of Pikhurko and Razborov.

Keywords

Cite

@article{arxiv.2311.18753,
  title  = {A note on extremal constructions for the Erd\H{o}s--Rademacher problem},
  author = {Xizhi Liu and Oleg Pikhurko},
  journal= {arXiv preprint arXiv:2311.18753},
  year   = {2024}
}

Comments

revised according to referee's suggestions

R2 v1 2026-06-28T13:37:19.561Z