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Let S n denote the symmetric group of all permutations of {1, 2,. .. , n} and let S = ∪ n≥0 S n. If Π ⊆ S is a set of permutations, then we let Av n (Π) be the set of permutations in S n which avoid every permutation of Π in the sense of pattern avoidance. One of the celebrated notions in pattern theory is that of Wilf-equivalence, where Π and Π are Wilf(More)
Ascent sequences were introduced by Bousquet-Mélou, Claesson, Dukes and Ki-taev in their study of (2 + 2)-free posets. An ascent sequence of length n is a nonneg-ative integer sequence x = x 1 x 2. .. x n such that x 1 = 0 and x i asc(x 1 x 2. .. x i−1)+ 1 for all 1 < i n, where asc(x 1 x 2. .. x i−1) is the number of ascents in the sequence x 1 x 2. .. x(More)
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