The clique density theorem

• 成果类型: Article
• 署名作者: Reiher, Christian
• 刊物名称: ANNALS OF MATHEMATICS
• ISSN/ISSBN: 0003-486X
• DOI: 10.4007/annals.2016.184.3.1
• 发表日期: 2016
• 页码: 683-707
• 关键词: triangles; number; graphs

摘要

Turan's theorem is a cornerstone of extremal graph theory. It asserts that for any integer r >= 2, every graph on n vertices with more than r-2/2(r-1) . n(2) edges contains a clique of size r, i.e., r mutually adjacent vertices. The corresponding extremal graphs are balanced (r - 1)-partite graphs. The question as to how many such r-cliques appear at least in any n-vertex graph with gamma n(2) edges has been intensively studied in the literature. In particular, Lovasz and Simonovits conjectured in the 1970's that asymptotically the best possible lower bound is given by the complete multipartite graph with 7712 edges in which all but one vertex class is of the same size while the remaining one may be smaller. Their conjecture was recently resolved for r = 3 by Razborov and for r = 4 by Nikiforov. In this article, we prove the conjecture for all values of r.