Deodhar's inequality for the double-affine Bruhat order

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Let WTW_{\mathcal{T}} be the double-affine Weyl monoid, let Δ~+\widetilde{\Delta}^+ denote the positive double-affine real roots, and let ℓ\ell be the length function. Deodhar's inequality. If x,y,z∈WTx,y,z\in W_{\mathcal{T}} satisfy x≤y≤zx\leq y\leq z, then

#{β[n]∈Δ~+∣x≤ysβ[n]≤z}≥ℓ(z)−ℓ(x).\#\{\beta[n]\in\widetilde{\Delta}^+\mid x\leq ys_{\beta[n]}\leq z\}\geq\ell(z)-\ell(x).

In finite and single-affine cases, the analogous inequality was conjectured by Deodhar and has since been proved by many authors. Its validity in the double-affine setting is the unresolved assertion made here.

References

Primary source

Dinakar Muthiah and Daniel Orr, “On the double-affine Bruhat order: the ε=1 conjecture and classification of covers in ADE type”, arXiv:1609.03653 (2016).

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