The alternating and c-noncrossing face conjecture for prepolypositroids

Let WW be a Weyl group, let cc be a Coxeter element, and let PP be a generic simple (W,c)(W,c)-prepolypositroid. Let R~\widetilde R be the associated set of transformed roots, and let (β~,γ~)R~(\widetilde\beta,\widetilde\gamma)\in\widetilde R span a two-dimensional face of the normal fan of PP. Two roots (β,γ)(\beta,\gamma) are alternating when (β,γ)=(γ,β)0(\beta,\gamma)=(\gamma,\beta)\geq 0, and they are cc-noncrossing when either (γ,β~)=0(\gamma^\vee,\widetilde\beta)=0 or (β,γ~)=0(\beta^\vee,\widetilde\gamma)=0.

Alternating and c-noncrossing face conjecture. If (β~,γ~)R~(\widetilde\beta,\widetilde\gamma)\in\widetilde R span a two-dimensional face of the normal fan of PP, then (β,γ)(\beta,\gamma) must be alternating and cc-noncrossing.

This conjecture predicts a necessary combinatorial condition on pairs of roots associated with two-dimensional faces of normal fans of generic simple (W,c)(W,c)-prepolypositroids. The supplied text gives no resolution status.

Sources & referencesView supporting material

Primary source

Thomas Lam and Alexander Postnikov, “Polypositroids”, arXiv:2010.07120 (2020).

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