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arXiv · 0711.3468

The sphericity of the complex of non-degenerate subspaces

Alice Devillers·Ralf Köhl·Bernhard Muhlherr
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Abstract

We prove that the complex of proper non-trivial non-degenerate subspaces of a finite-dimensional vector space endowed with a non-degenerate sesquilinear form is homotopy equivalent to a wedge of spheres. Additionally, we show that the same is true for a slight generalization, the so-called generalized Phan geometries of type A_n. These generalized Phan geometries occur as relative links of certain filtrations. Their sphericity implies finiteness properties of suitable arithmetic groups and allows for a revision of Phan's group-theoretical local recognition of suitable finite groups of Lie type with simply laced diagram.

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Alice Devillers, Ralf Köhl, Bernhard Muhlherr. 2007-11-21. The sphericity of the complex of non-degenerate subspaces. https://arxiv.org/abs/0711.3468

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