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LOW-DEGREE BOOLEAN FUNCTIONS ON $S_{n}$, WITH AN APPLICATION TO ISOPERIMETRY

Part of: Extremal combinatorics

Published online by Cambridge University Press:  03 October 2017

DAVID ELLIS ,
YUVAL FILMUS  and
EHUD FRIEDGUT
DAVID ELLIS
Affiliation:
School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK; d.ellis@qmul.ac.uk
YUVAL FILMUS
Affiliation:
Computer Science Department, Technion – Israel Institute of Technology, Technion City, Haifa 3200003, Israel; yuvalfi@cs.technion.ac.il
EHUD FRIEDGUT
Affiliation:
Faculty of Mathematics and Computer Science, Weizmann Institute of Science, Rehovot 76100, Israel; ehud.friedgut@weizmann.ac.il

Abstract

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We prove that Boolean functions on $S_{n}$, whose Fourier transform is highly concentrated on irreducible representations indexed by partitions of $n$ whose largest part has size at least $n-t$, are close to being unions of cosets of stabilizers of $t$-tuples. We also obtain an edge-isoperimetric inequality for the transposition graph on $S_{n}$ which is asymptotically sharp for subsets of $S_{n}$ of size $n!/\text{poly}(n)$, using eigenvalue techniques. We then combine these two results to obtain a sharp edge-isoperimetric inequality for subsets of $S_{n}$ of size $(n-t)!$, where $n$ is large compared to $t$, confirming a conjecture of Ben Efraim in these cases.

MSC classification

Primary: 05D05: Extremal set theory
Type
Research Article
Information
Forum of Mathematics, Sigma , Volume 5 , 2017 , e23
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Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
© The Author(s) 2017

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