Note: Multiple cross-intersecting families of signed sets

  • Authors:
  • Peter Borg;Imre Leader

  • Affiliations:
  • Department of Mathematics, University of Malta, Msida MSD 2080, Malta;Department of Pure Mathematics and Mathematical Statistics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WB, United Kingdom

  • Venue:
  • Journal of Combinatorial Theory Series A
  • Year:
  • 2010

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Abstract

A k-signed r-set on[n]={1,...,n} is an ordered pair (A,f), where A is an r-subset of [n] and f is a function from A to [k]. Families A"1,...,A"p are said to be cross-intersecting if any set in any family A"i intersects any set in any other family A"j. Hilton proved a sharp bound for the sum of sizes of cross-intersecting families of r-subsets of [n]. Our aim is to generalise Hilton's bound to one for families of k-signed r-sets on [n]. The main tool developed is an extension of Katona's cyclic permutation argument.