Cover image for Isomorphism Problem In Coxeter Groups.
Isomorphism Problem In Coxeter Groups.
Title:
Isomorphism Problem In Coxeter Groups.
Author:
Bahls, Patrick.
ISBN:
9781860947193
Personal Author:
Physical Description:
1 online resource (192 pages)
Contents:
Preface -- Contents -- Chapter 1 Preliminaries on Coxeter groups -- 1.1 Historical background and motivation -- 1.2 Coxeter systems and Coxeter groups -- 1.2.1 A combinatorial definition -- 1.2.2 A geometric definition -- 1.2.3 Examples -- 1.3 Basic properties of Coxeter groups -- 1.3.1 Reflections -- 1.3.2 Lengths of words and geodesics -- 1.3.3 Parabolic subgroups -- 1.3.4 The Deletion Condition -- 1.4 Van Kampen diagrams -- 1.5 Other geometric viewpoints: the Coxeter complex and the Davis complex -- 1.5.1 Simplicial complexes -- 1.5.2 The Coxeter complex -- 1.5.3 The Davis complex -- 1.5.4 The metric on -- 1.6 Exercises -- Chapter 2 Further properties of Coxeter groups -- 2.1 The (co)homology of a Coxeter group -- 2.1.1 Group (co)homology -- 2.1.2 Poincaré duality -- 2.2 Normalizers and centralizers -- 2.2.1 The normalizer of a parabolic subgroup -- 2.2.2 Centralizers in Coxeter groups -- 2.3 Visual decompositions of Coxeter groups -- 2.3.1 Graph-of-groups decompositions -- 2.3.2 Visual decompositions -- 2.4 The Word and Conjugacy Problems -- 2.5 Exercises -- Chapter 3 Rigidity -- 3.1 Rigidity and related conditions -- 3.1.1 Rigidity and strong rigidity -- 3.1.2 Reflection independence -- 3.1.3 Reflection rigidity and strong reflection rigidity -- 3.1.4 Classes of Coxeter groups -- 3.2 Some first results -- 3.2.1 Right-angled Coxeter groups -- 3.2.2 The role of reflections -- 3.3 Even Coxeter groups -- 3.4 Large-type and two-dimensional Coxeter groups -- 3.5 Related issues -- 3.5.1 Automorphisms of right-angled Coxeter groups -- 3.5.2 Automorphisms of more general Coxeter groups -- 3.5.3 Artin groups -- 3.6 Exercises -- Chapter 4 In the beginning: some early results -- 4.1 Rigidity of right-angled Coxeter groups -- 4.2 A slight generalization -- 4.3 Strong rigidity through homological conditions -- 4.3.1 The conditions HMn and PMn.

4.3.2 Fixed point sets and the nerve of (W, S) -- 4.3.3 The action of (W, S') on -- 4.3.4 Completing the proof -- 4.3.5 Aut(W) -- 4.4 Two-dimensional groups -- 4.5 Exercises -- Chapter 5 Even Coxeter groups -- 5.1 The structure of even Coxeter groups -- 5.2 Conjugate simplices in even systems -- 5.3 Reflection rigidity in even groups -- 5.4 Reflection preservation and reflection independence -- 5.5 The Isomorphism Problem for even Coxeter groups -- 5.5.1 The algorithm -- 5.5.2 Matching edges between even and non-even diagrams -- 5.5.3 Finding u" -- 5.6 Exercises -- Chapter 6 More general groups -- 6.1 Large-type Coxeter systems -- 6.1.1 The chamber system associated to a Coxeter system -- 6.1.2 The chamber system Ch(W, S) and reflection subgroups of W -- 6.1.3 Universal root systems -- 6.1.4 The first case: V is edge-connected -- 6.1.5 The general case: applying visual decompositions -- 6.2 Circuits and centralizers -- 6.2.1 Walking around a circuit -- 6.2.2 Centralizer chasing in even Coxeter systems -- 6.2.3 The first case: V is a simple circuit -- 6.2.4 The general case -- 6.3 Exercises -- Chapter 7 Refinements and generalizations: automorphisms and Artin groups -- 7.1 Automorphisms of right-angled groups -- 7.1.1 The group Spe(W) -- 7.1.2 What does Spe(W) look like? -- 7.2 Coxeter systems with V complete -- 7.2.1 A chain of subgroups of Aut(W) -- 7.2.2 The first step -- 7.2.3 The second step -- 7.2.4 A quick aside: properties of the Tits cone -- 7.2.5 The proof of Theorem 7.4 -- 7.3 Dehn twists and decompositions: Aut(W) for some large-type groups -- 7.3.1 Centralizer chasing and visual decompositions: reprise -- 7.3.2 The ratios of conjugating elements -- 7.3.3 The unit graph and the structure of an automorphism -- 7.4 Artin groups -- 7.4.1 Rigidity of Artin groups -- 7.4.2 Automorphisms of Artin groups -- 7.5 Exercises -- Bibliography -- Index.
Abstract:
The book is the first to give a comprehensive overview of the techniques and tools currently being used in the study of combinatorial problems in Coxeter groups. It is self-contained, and accessible even to advanced undergraduate students of mathematics. The primary purpose of the book is to highlight approximations to the difficult isomorphism problem in Coxeter groups. A number of theorems relating to this problem are stated and proven. Most of the results addressed here concern conditions which can be seen as varying degrees of uniqueness of representations of Coxeter groups. Throughout the investigation, the readers are introduced to a large number of tools in the theory of Coxeter groups, drawn from dozens of recent articles by prominent researchers in geometric and combinatorial group theory, among other fields. As the central problem of the book may in fact be solved soon, the book aims to go further, providing the readers with many techniques that can be used to answer more general questions. The readers are challenged to practice those techniques by solving exercises, a list of which concludes each chapter.
Local Note:
Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, 2017. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries.
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