Counting subgraphs in quasi-random 4-uniform hypergraphs

  • Authors:
  • Vojtĕch Rödl;Jozef Skokan

  • Affiliations:
  • Emory University, Atlanta, Georgia 30322;University of Illinois at Urbana–Champaign, 1409 West Green Street, Urbana, Illinois 61801 and Instituto de Matemática e Estatística, Universidade de São Paulo, Rua do Mat ...

  • Venue:
  • Random Structures & Algorithms - Proceedings of the Eleventh International Conference "Random Structures and Algorithms," August 9—13, 2003, Poznan, Poland
  • Year:
  • 2005

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Abstract

A bipartite graph G = (V1 ∪ V2, E) is (&dgr;, d)-regular if $$|d-d(V^{\prime}_{1}, V^{\prime}_{2})| G = (V1 ∪ V2 ∪ V3, E) is a 3-partite graph whose restrictions on V1 ∪ V2, V1 ∪ V3, V2 ∪ V3 are (&dgr;, d)-regular, then G contains $(d^{3} \pm f(\delta))|V_{1}||V_{2}||V_{3}|$ copies of K3. This fact and its various extensions are the key ingredients in most applications of Szemerédi's Regularity Lemma. To derive a similar results for r-uniform hypergraphs, r 2, is a harder problem. In 1994, Frankl and Rödl developed a regularity lemma and counting argument for 3-uniform hypergraphs. In this paper, we exploit their approach to develop a counting argument for 4-uniform hypergraphs. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2005