Abstract
We define combinatorially a partial order on the set partitions and show that it is equivalent to the Bruhat-Chevalley-Renner order on the upper triangular matrices. By considering subposets consisting of set partitions with a fixed number of blocks, we introduce and investigate “Stirling posets.” As we show, the Stirling posets have a hierarchy and they glue together to give the whole set partition poset. Moreover, we show that they (Stirling posets) are graded and EL-shellable. We offer various reformulations of their length functions and determine the recurrences for their length generating series.
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Can, M.B., Cherniavsky, Y. Stirling posets. Isr. J. Math. 237, 185–219 (2020). https://doi.org/10.1007/s11856-020-2004-1
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DOI: https://doi.org/10.1007/s11856-020-2004-1