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arXiv · 2408.05015

An algebraic approach to Erd\H{o}s-Ko-Rado sets of flags in spherical buildings II

Jan De Beule·Sam Mattheus·Klaus Metsch
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Abstract

We continue our investigation of Erd\H{o}s-Ko-Rado (EKR) sets of flags in spherical buildings. In previous work, we used the theory of buildings and Iwahori-Hecke algebras to obtain upper bounds on their size. As the next step towards the classification of the maximal EKR-sets, we describe the eigenspaces for the smallest eigenvalue of the opposition graphs. We determine their multiplicity and provide a combinatorial description of spanning sets of these subspaces, from which a complete description of the maximal Erd\H{o}s-Ko-Rado sets of flags may potentially be found. This was recently shown to be possible for type $A_n$, $n$ odd, by Heering, Lansdown, and the last author by making use of the current work.

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Jan De Beule, Sam Mattheus, Klaus Metsch. 2024-08-09. An algebraic approach to Erd\H{o}s-Ko-Rado sets of flags in spherical buildings II. https://arxiv.org/abs/2408.05015

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