The cycle characterization conjecture for cyclically fully commutative elements in type A

Let W(An)W(A_n) be the Coxeter group of type AnA_n, identified with the symmetric group Sn+1S_{n+1}, and let wW(An)w\in W(A_n) correspond to a permutation with disjoint cycles c1,c2,,ckc_1,c_2,\ldots,c_k. Write each cjc_j with its smallest number first. A cycle has connected support if the set of numbers appearing in it consists of consecutive numbers, and it has a direction change at w(i)w(i) if either i<w(i)i<w(i) and w(i)>w2(i)w(i)>w^2(i), or i>w(i)i>w(i) and w(i)<w2(i)w(i)<w^2(i). The cycle characterization conjecture. The element ww is cyclically fully commutative if and only if every cycle cjc_j has connected support and has at most one direction change. This conjecture gives a direct criterion for recognizing cyclically fully commutative elements from the cycle decomposition of the corresponding permutation; the authors report computational evidence from Sage but do not establish the assertion in general.

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Primary source

Brooke Fox, “Conjugacy classes of cyclically fully commutative elements in Coxeter groups of type A”, arXiv:1506.02299 (2015).

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