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A Construction of Almost Steiner Systems
Authors:Asaf Ferber  Rani Hod  Michael Krivelevich  Benny Sudakov
Affiliation:1. School of Mathematical Sciences, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel;2. School of Computer Science, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel;3. Department of Mathematics, ETH, Zurich, Switzerland;4. Department of Mathematics, UCLA, Los Angeles, California
Abstract:Let n, k, and t be integers satisfying urn:x-wiley:10638539:media:jcd21380:jcd21380-math-0001. A Steiner system with parameters t, k, and n is a k‐uniform hypergraph on n vertices in which every set of t distinct vertices is contained in exactly one edge. An outstanding problem in Design Theory is to determine whether a nontrivial Steiner system exists for urn:x-wiley:10638539:media:jcd21380:jcd21380-math-0002. In this note we prove that for every urn:x-wiley:10638539:media:jcd21380:jcd21380-math-0003 and sufficiently large n, there exists an almost Steiner system with parameters t, k, and n; that is, there exists a k‐uniform hypergraph on n vertices such that every set of t distinct vertices is covered by either one or two edges.
Keywords:Steiner systems
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