Pattern-avoidance characterization of lci K-orbit closures

Let G=GL(p+q,C)G=GL(p+q,\mathbb{C}), K=GL(p,C)×GL(q,C)K=GL(p,\mathbb{C})\times GL(q,\mathbb{C}), and consider KK-orbit closures in G/BG/B, indexed by clans. A clan avoids a pattern when it contains no occurrence of that pattern, with negatives of patterns included when specified. Pattern-avoidance conjecture for lci K-orbit closures. LCI-ness of KK-orbit closures for (GL(p+q,C),GL(p,C)×GL(q,C))(GL(p+q,\mathbb{C}),GL(p,\mathbb{C})\times GL(q,\mathbb{C})) is characterized by pattern avoidance. In other words, a KK-orbit closure is lci if and only if its indexing clan avoids the patterns that characterize lci-ness. Computations verify the characterization through p+q8p+q\leq 8, but the authors do not claim that the displayed finite list of additional bad patterns is complete; the conjecture remains open because checks at p+q=9p+q=9 were unavailable.

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Primary source

Alexander Woo and Benjamin J. Wyser, “Combinatorial results on (1,2,1,2)-avoiding GL(p,C) GL(q,C)-orbit closures on GL(p+q, C)/B”, arXiv:1403.0363 (2014).

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