The Lefschetz condition conjecture for Braden–MacPherson sheaves

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Let w∈W^w\in{\widehat{\mathcal W}} and suppose that char⁡K>N(w)\operatorname{char} K>N(w). For every x≤wx\le w, let

ix ⁣:B‾(w)x→B‾(w)xi_x\colon\overline{\mathcal B}(w)_x\to\overline{\mathcal B}(w)^x

be the indicated map between the costalk and stalk of the reduced Braden–MacPherson sheaf. Recall that a map f ⁣:A→Bf\colon A\to B of graded free K[t]K[t]-modules satisfies the Lefschetz condition with center l∈Zl\in\mathbb Z if multiplication by tnt^n induces an isomorphism

(coker⁡f){l−n}→∼(coker⁡f){l+n}(\operatorname{coker}f)_{\{l-n\}}\stackrel{\sim}{\to}(\operatorname{coker}f)_{\{l+n\}}

for every n≥1n\ge1. The Lefschetz condition conjecture. For all x≤wx\le w, the map ixi_x satisfies the Lefschetz condition with center l(w)l(w). This conjecture proposes a Hard Lefschetz-type symmetry for the stalk–costalk maps of Braden–MacPherson sheaves in characteristic greater than N(w)N(w). The supplied text does not state whether it has been resolved.

References

Primary source

Peter Fiebig, “An upper bound on the exceptional characteristics for Lusztig's character formula”, arXiv:0811.1674 (2009).

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