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Posets in which every interval is a product of chains, and natural local actions of the symmetric group

✍ Scribed by David J. Grabiner


Publisher
Elsevier Science
Year
1999
Tongue
English
Weight
545 KB
Volume
199
Category
Article
ISSN
0012-365X

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✦ Synopsis


Consider a graded poset P with maximal and minimal elements. If every interval of rank three in P is a product of chains, and for every interval [.L ~1 of rank at least four, the open interval (x, y) is connected, we show that the entire poset is a product of chains. This proves a conjecture of Stanley concerning the natural local action of the symmetric group on maximal chains in a graded poset. On a product of chains, the natural action is the permutation action on the multiset corresponding to the chains. The result implies that if every open interval is connected (which holds if the poset is Cohen-Macaulay, for example), the only possible such natural action is this multiset action.