Table of Contents
Introduction v
Part I: Stallings's theorem about pregroups;
introduction to pregroups of finite height
1. The definition of a pregroup 1
2. The pregroups of finite height 5
3. The subpregroup of units 13
Part II: A presentation for the universal group
of a pregroup of finite height.
4. Pregroup actions and generating sets 20
5. A presentation for the universal group of a
pregroup of finite height 29
Part III: The relationship between pregroups
and graphs of groups
6. A graph of groups structure for pregroups
of finite height 39
7. A pregroup structure for graphs
of groups of finite diameter 55
References 73
in
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