Discrete Mathematics & Theoretical Computer Science

DMTCS

Volume 6 n° 2 (2004), pp. 461-470


author:Toufik Mansour
title:On an open problem of Green and Losonczy: exact enumeration of freely braided permutations
keywords:restricted permutations, freely braided permutations, generating functions
abstract:Recently, Green and Losonczy GL1,GL2 introduced freely braided permutation as a special class of restricted permutations has arisen in representation theory. The freely braided permutations were introduced and studied as the upper bound for the number of commutation classes of reduced expressions for an element of a simply laced Coxeter group is achieved if and only if when the element is freely braided. In this paper, we prove that the generating function for the number of freely braided permutations in Sn is given by
1-3x-2x2+(1+x)√1-4x
1-4x-x2+(1-x2)√1-4x

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reference: Toufik Mansour (2004), On an open problem of Green and Losonczy: exact enumeration of freely braided permutations, Discrete Mathematics and Theoretical Computer Science 6, pp. 461-470
bibtex:For a corresponding BibTeX entry, please consider our BibTeX-file.
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