Extremal problems in uniformly dense hypergraphs. (August 2020)

• Record Type: Journal Article
• Authors: Reiher, Christian
• Is Part Of: European journal of combinatorics. Volume 88(2020)
• Publication Date: 2020-08
• Subjects: Combinatorial analysis -- Periodicals; Analyse combinatoire -- Périodiques; Combinatorial analysis; Periodicals; Electronic journals; 511.6
• DOI: 10.1016/j.ejc.2020.103117
• Languages: English
• ISSNs: 0195-6698

Abstract

Abstract: For a k -uniform hypergraph F let ex ( n, F ) be the maximum number of edges of a k -uniform n -vertex hypergraph H which contains no copy of F . Determining or estimating ex ( n, F ) is a classical and central problem in extremal combinatorics. While for graphs ( k = 2 ) this problem is well understood, due to the work of Mantel, Turán, Erdős, Stone, Simonovits and many others, only very little is known for k -uniform hypergraphs for k > 2 . Already the case when F is a k -uniform hypergraph with three edges on k + 1 vertices is still wide open even for k = 3 . We consider variants of such problems where the large hypergraph H enjoys additional hereditary density conditions. Questions of this type were suggested by Erdős and Sós about 30 years ago. In recent work with Rödl and Schacht it turned out that the regularity method for hypergraphs, established by Gowers and by Rödl et al. about a decade ago, is a suitable tool for extremal problems of this type and we shall discuss some of those recent results and some interesting open problems in this area.