Abstract
We extend properties of the weak order on finite Coxeter groups to Weyl groupoids admitting a finite root system. In particular, we determine the topological structure of intervals with respect to weak order, and show that the set of morphisms with fixed target object forms an ortho-complemented meet semilattice. We define the Coxeter complex of a Weyl groupoid with finite root system and show that it coincides with the triangulation of a sphere cut out by a simplicial hyperplane arrangement. As a consequence, one obtains an algebraic interpretation of many hyperplane arrangements that are not reflection arrangements.
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I.H. was supported by the German Research Foundation via a Heisenberg fellowship.
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Heckenberger, I., Welker, V. Geometric combinatorics of Weyl groupoids. J Algebr Comb 34, 115–139 (2011). https://doi.org/10.1007/s10801-010-0264-2
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DOI: https://doi.org/10.1007/s10801-010-0264-2