Extra-special orbit and Lagrangian-ideal conjecture

In the extra-special case, let XΔ(1)\mathfrak X_{\Delta(1)} be the reverse operator on the associated weight poset, let Πl\Pi_l be the set of long simple roots, and let hh be the Coxeter number.

Extra-special orbit conjecture. The number of XΔ(1)\mathfrak X_{\Delta(1)}-orbits is #Πl\#\Pi_l, every orbit has size h1h-1, and, if hh is even, every orbit contains a unique Lagrangian upper ideal.

The orbit count and orbit size are suggested by the proved enumeration in the extra-special case and explicit calculations; the statement is verified in several types but remains open in general.

Sources & referencesView supporting material

Primary source

Dmitri I. Panyushev, “Antichains in weight posets associated with gradings of simple Lie algebras”, arXiv:1411.7683 (2014).

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