Finite Presentability of S-Arithmetic Groups Compact Presentability of Solvable Groups

The problem of determining which S-arithmetic groups have a finite presentation is solved for arbitrary linear algebraic groups over finite extension fields of #3. For certain solvable topological groups this problem may be reduced to an analogous problem

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1261 Herbert Abels

Finite Presentability of S-Arithmetic Groups Compact Presentability of Solvable Groups

Springer-Verlag Berlin Heidelberg New York London Paris Tokyo

Lecture Notes in Mathematics Edited by A. Dold and B. Eckmann

1261 Herbert Abels

Finite Presentability of S-Arithmetic Groups Compact Presentability of Solvable Groups

Springer-Verlag Berlin Heidelberg New York London Paris Tokyo

Author

Herbert Abels Universitat Bielefeld, Fakultat fur Mathematik 4800 Bielefeld, Federal Republic of Germany

Mathematics Subject Classification (1980): Primary: 20F05, 20G30, 20G25, 22D05, 20F 16 Secondary: 20F 18, 20G 10, 20G35, 11 E99, 17B55, 20J05, 22E99 ISBN 3-540-17975-5 Springer-Verlag Berlin Heidelberg New York ISBN 0-387 -17975-5 Springer-Verlag New York Berlin Heidelberg

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9, 1965, in its version of June 24, 1985, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law.

© Springer-Verlag Berlin Heidelberg 1987 Printed in Germany Printing and binding: Druckhaus Beltz, Hemsbach/Bergstr. 2146/3140-543210

Fur Elisabeth

CONTENTS

O.

I.

Introduction 0.1

Abstract

1

0.2

The problem and its solution

1

0.3

Survey of the proof, contents of the chapters

8

0.4

More general questions

11

0.5

Acknowledgements . .

13

.

Compact presentability and contracting automorphisms

15 15

1.1

Compact presentability

1.2

Contracting automorphisms

17

1.3

Compact presentability and contracting automorphisms

23

II. Filtrations of Lie algebras and groups

27

2.1

Filtered Lie algebras.

27

2.2

Formulae on commutators

30

2.3

Filtered groups.

31

.

. .

2.4

Some results about nilpotent groups

33

2.5

Nilpotent Lie groups over fields of characteristic zero

36

2.6

Nilpotent Lie groups over p-adic fields.

44

.

III. A necessary condition for compact presentability . .

.

.

. .

49

3.1

Weights.

.

50

3.2

Values of weights

52

3.3

A counterexample

56

3.4

The geometric invariant of Bieri and Strebel

59 61

IV. Implications of the necessary condition 4.1 The building blocks NC 4.2

The colimits

4.3

Commutators in

Hand

4.4

The descending central series of

62 64

M

68

n M

71

VI

4.5 4.6 4.7 V.

80

H changed into a top logical group H U The kernel of H Q N U The colimit of the Lie algebras n C

The second homology . . .

83

87 .

90

.

93

5. 1

Homology of a group. The Hopf extension

5.2

Homology of a Lie algebra

5.3

Lie algebra homology versus group homology

5.4

A topology on the Hopf extension

102

5.5

107

5.6

H H 2(nlmp)o 2(n!K)o The main theorem

111

5.7

Examples

115

VI. S-arithmetic groups