Published August 2008 | Version public
Journal Article

Erdős–Ko–Rado theorems for permutations and set partitions

  • 1. ROR icon California Institute of Technology

Abstract

Let Sym([n]) denote the collection of all permutations of [n]={1,…,n}. Suppose A⊆Sym([n]) is a family of permutations such that any two of its elements (when written in its cycle decomposition) have at least t cycles in common. We prove that for sufficiently large n, |A|⩽(n−t)! with equality if and only if A is the stabilizer of t fixed points. Similarly, let B(n) denote the collection of all set partitions of [n] and suppose A⊆B(n) is a family of set partitions such that any two of its elements have at least t blocks in common. It is proved that, for sufficiently large n, |A|⩽B_(n−t) with equality if and only if A consists of all set partitions with t fixed singletons, where B_n is the nth Bell number.

Additional Information

© 2008 Elsevier Inc. Received 4 June 2007, Available online 30 January 2008. We thank the anonymous referees for their comments that helped us make several improvements to this paper.

Additional details

Identifiers

Eprint ID
80707
DOI
10.1016/j.jcta.2007.12.004
Resolver ID
CaltechAUTHORS:20170822-155141742

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2017-08-23
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2021-11-15
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