An algebraic approach to Erdős-Ko-Rado sets of flags in spherical buildings

Jan De Beule, Sam Mattheus, Klaus Metsch

Onderzoeksoutput: Articlepeer review

2 Citaten (Scopus)


In this paper, oppositeness in spherical buildings is used to define an EKR-problem for flags in projective and polar spaces. A novel application of the theory of buildings and Iwahori-Hecke algebras is developed to prove sharp upper bounds for EKR-sets of flags. In this framework, we can reprove and generalize previous upper bounds for EKR-problems in projective and polar spaces. The bounds are obtained by the application of the Delsarte-Hoffman coclique bound to the opposition graph. The computation of its eigenvalues is due to earlier work by Andries Brouwer and an explicit algorithm is worked out. For the classical geometries, the execution of this algorithm boils down to elementary combinatorics. Connections to building theory, Iwahori-Hecke algebras, classical groups and diagram geometries are briefly discussed. Several open problems are posed throughout and at the end.
Originele taal-2English
Pagina's (van-tot)1-33
Aantal pagina's33
TijdschriftJournal of Combinatorial Theory - Series A
StatusPublished - nov 2022

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© 2022 Elsevier Inc.

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