3 citations · 10 across the 17 of their papers we have counts for
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Pattern avoidance and the Bruhat order on involutions
Axel Hultman, Kathrin Vorwerk
We show that the principal order ideal below an element w in the Bruhat order on involutions in a symmetric group is a Boolean lattice if and only if w avoids the patterns 4321, 45…
From Bruhat intervals to intersection lattices and a conjecture of Postnikov
Axel Hultman, Svante Linusson, John Shareshian +1
We prove the conjecture of A. Postnikov that (A) the number of regions in the inversion hyperplane arrangement associated with a permutation $w\in \Sn$ is at most the number of ele…
Fixed points of zircon automorphisms
Axel Hultman
A zircon is a poset in which every principal order ideal is finite and equipped with a so-called special matching. We prove that the subposet induced by the fixed points of any aut…
Twisted identities in Coxeter groups
Axel Hultman
Given a Coxeter system (W,S) equipped with an involutive automorphism T, the set of twisted identities is i(T) = {T(w)^{-1}w : w \in W}. We point out how i(T) shows up in several c…