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arXiv · 1306.5926

On the M\"obius Function of Permutations With One Descent

Jason P Smith
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Abstract

The set of all permutations, ordered by pattern containment, is a poset. We give a formula for the M\"obius function of intervals $[1,\pi]$ in this poset, for any permutation $\pi$ with at most one descent. We compute the M\"obius function as a function of the number and positions of pairs of consecutive letters in $\pi$ that are consecutive in value. As a result of this we show that the M\"obius function is unbounded on the poset of all permutations. We show that the M\"obius function is zero on any interval $[1,\pi]$ where $\pi$ has a triple of consecutive letters whose values are consecutive and monotone. We also conjecture values of the M\"obius function on some other intervals of permutations with at most one descent.

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Jason P Smith. 2013-06-25. On the M\"obius Function of Permutations With One Descent. https://arxiv.org/abs/1306.5926

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