Abstract
With respect to a fixedn-element ordered setP, thegeneralized permutahedron Perm(P) is the set of all ordered setsP ∩L, whereL is any permutation of the elements of the underlyingn-element set. Considered as a subset of the extension lattice of ann-element set,Perm(P) is cover-preserving. We apply this to deduce, for instance, that, in any finite ordered setP, there is a comparability whose removal will not increase the dimension, and there is a comparability whose addition toP will not increase its dimension.
We establish further properties about the extension lattice which seem to be of independent interest, leading for example, to the characterization of those ordered setsP for which this generalized permutahedron is itself a lattice.
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Dedicated to the memory of Alan Day
Supported in part by PRC Mathématiques-Informatique (France) and NSERC (Canada).
Supported in part by DFG (Germany) and NSERC (Canada).
Supported in part by NSERC (Canada).
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Pouzet, M., Reuter, K., Rival, I. et al. A generalized permutahedron. Algebra Universalis 34, 496–509 (1995). https://doi.org/10.1007/BF01181874
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DOI: https://doi.org/10.1007/BF01181874