Pattern Avoidance and the Bruhat Order

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The structure of order ideals in the Bruhat order for the symmetric group is elucidated via permutation patterns. A method for determining non-isomorphic principal order ideals is described and applied for small lengths. The permutations with boolean principal order ideals are characterized. These form an order ideal which is a simplicial poset, and its rank generating function is computed. Moreover, the permutations whose principal order ideals have a form related to boolean posets are also completely described. It is determined when the set of permutations avoiding a particular set of patterns is an order ideal, and the rank generating functions of these ideals are computed. Finally, the Bruhat order in types B and D is studied, and the elements with boolean principal order ideals are characterized and enumerated by length.
18 pages, 7 figures

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Combinatorics, 05E15; 06A07; 05A05

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http://salesiana.dossiersoluciones.com/handle/123456789/111568

Consulte el texto completo en el siguiente enlace:

https://arxiv.org/abs/math/0604322
 http://arxiv.org/abs/math/0604322

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arXiv