Abstract

We survey results about computational complexity of the word problem in groups, Dehn functions of groups and related problems.

Highlights

  • The word and conjugacy problems are the most classical algorithmic problem for groups going back to the work of Dehn and Tietze at the beginning of the twentieth century

  • We present an algebraic characterization of groups with word problem in NP from [22] and groups with word problem in PSPACE from [183], discuss examples of groups with NP-complete [210] and coNP-complete [21] word problems

  • In [192], we showed that the group a, b, t1, t2 | ti ati−1 = ab, ti b = bti, i = 1, 2 has cubic Dehn function, linear isodiametric function and non- connected asymptotic cones

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Summary

Introduction

The word and conjugacy problems are the most classical algorithmic problem for groups going back to the work of Dehn and Tietze at the beginning of the twentieth century. There are very many papers devoted to these problems for various classes of groups Different aspects of these problems are discussed in many books and surveys (see, for example, [24,35,50,72,78,91,137,147,162,181,187,207,208]). Several new methods are used in the proofs of these results and our goal in this survey is to give as gentle as possible an introduction to these results and methods To this end, we often present not the results in their full generality but their easier to explain approximations. There is a nice recent survey by Shpilrain [219] where at least some of these topics are discussed

Algorithmic problems in groups
Van Kampen diagrams
The computational complexity and algebraic systems
Isoperimetric and isodiametric functions of groups
Filling length functions and the space complexity
Two examples of Dehn functions
Isoperimetric functions of geodesic metric spaces: different area functions
Cayley complexes and metric spaces
The Dehn functions of groups acting on metric spaces
2.10 Asymptotic cones of metric spaces and groups
2.11 Asymptotic cones and Dehn functions
Hyperbolic groups and asymptotic cones
Nilpotent groups
Semihyperbolic groups
Dehn functions and algorithmic properties of groups
NP-complete and coNP-complete groups
Higman embedding
Methods
Open problems
Full Text
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