Jean Yeh

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The symmetry of the joint distribution of the numbers of crossings and nestings of length 2 has been observed in many combinatorial structures, including permutations , matchings, set partitions, linked partitions, and certain families of graphs. These results have been unified in the larger context of enumeration of northeast and southeast chains of length(More)
In this paper, we focus on a " local property " of permutations: value-peak. A permutation σ has a value-peak σ(i) if σ(i − 1) < σ(i) > σ(i + 1) for some i ∈ [2, n − 1]. Define V P (σ) as the set of value-peaks of the permutation σ. For any S ⊆ [3, n], define V P n (S) such that V P (σ) = S. Let P n = {S | V P n (S) = ∅}. we make the set P n into a poset P(More)
The circular peak set of a permutation σ is the set {σ(i) | σ(i−1) < σ(i) > σ(i+1)}. In this paper, we focus on the enumeration problems for permutations by circular peak sets. Let cp n (S) denote the number of the permutations of order n which have the circular peak set S. For the case with |S| = 0, 1, 2, we derive the explicit formulas for cp n (S). We(More)
In this paper, let P l n;≤s;k denote a set of k-flaw preference sets (a 1 ,. .. , a n) with n parking spaces satisfying that 1 ≤ a i ≤ s for any i and a 1 = l and p l We use a combinatorial approach to the enumeration of k-flaw preference sets by their leading terms. The approach relies on bijections between the k-flaw preference sets and labeled rooted(More)
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