Parabolic aligned elements form a lattice quotient of parabolic weak order

From papers

Let (W,S)(W,S) be a finite Coxeter system, let JSJ\subseteq S, and let cWc\in W be a Coxeter element. An element of WJW^J is (WJ,c)(W^J,c)-aligned if, whenever tα<taα+bβ<tβt_{\alpha}<t_{a\alpha+b\beta}<t_{\beta} in Inv(wJ(c))\operatorname{Inv}(\mathbf{w_{\circ}^{J}(c)}), where α,βΦ+\alpha,\beta\in\Phi^{+} and a,ba,b are positive integers, the condition taα+bβCov(w)t_{a\alpha+b\beta}\in\operatorname{Cov}(w) implies tαInv(w)t_{\alpha}\in\operatorname{Inv}(w). Write Align(WJ,c)\operatorname{Align}(W^J,c) for the set of such elements, and let Weak(Align(WJ,c))\operatorname{Weak}(\operatorname{Align}(W^J,c)) denote the weak-order poset on this set. Parabolic lattice conjecture. For any finite Coxeter system (W,S)(W,S), any JSJ\subseteq S, and any Coxeter element cWc\in W, the poset

Weak(Align(WJ,c))\operatorname{Weak}\bigl(\operatorname{Align}(W^{J},c)\bigr)

is a lattice. Moreover, it is a lattice quotient of Weak(WJ)\operatorname{Weak}(W^{J}). This would extend the known parabolic Tamari-lattice result from the symmetric group to arbitrary finite Coxeter systems and parabolic quotients; the claim was motivated by computer experiments, but no resolution is supplied here.

Progress summary

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Sources & referencesView supporting material

Primary source

Henri Mühle and Nathan Williams, “Tamari Lattices for Parabolic Quotients of the Symmetric Group”, arXiv:1804.02761 (2019).

Solutions 0

No solutions have been posted yet.