Tame Algebras and Integral Quadratic Forms

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1099

Claus Michael Ringel

Tame Algebras and Integral Quadratic Forms

Spri nger-Verlag Berlin Heidelberg New York Tokyo 1984

Author

Claus Michael Ringel Fakultat fOr Mathematik, Universitat Bielefeld Postfach 8640, 4800 Bielefeld, Federal Republic of Germany

AMS Subject Classification (1980): 05C20, 06A10, 10B05, 15A30, 16A46, 16A48, 16A62, 16A64, 16-02, 18E10 ISBN 3-540-13905-2 Springer-Verlag Berlin Heidelberg New York Tokyo ISBN 0-387-13905-2 Springer-Verlag New York Heidelberg Berlin Tokyo

This work IS subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private use, a fee is payable to "Verwertungsgesellschaft Wort", Munich.

© by Springer-Verlag Berlin Heidelberg 1984 Printed in Germany Printing and binding: Beltz Offsetdruck, Hemsbach/Bergstr. 2146/3140-543210

TAB LEO F

CON TEN T S

Introduction Integral quadratic forms 1.0 1.1

Two theorems of Ovsienko Roots of an integral quadratic form derivatives

DiX

of

X

and the partial

2

X

7

1.2

Dynkin graphs and Euclidean graphs

1.3

Graphical forms

II

1.4

Reduction to graphical forms

14

1.5

The quadratic forms occurring in tables I and 2

18

1.6

Maximal sincere positive roots of graphical forms with a unique exceptional index

22

1.7

Completeness of table

24

1.8

Proof of theorem 2

30

1.9

Completeness of table 2

31

1.10

The extended quadratic form of a finite partially ordered set

35

2

Quivers, module categories, subspace categories (notation, results, some proofs)

41 42

2.1

Quivers and translation quivers

2.2

Krull-Schmidt k-categories

52

2.3

Exact categories

59

2.4

Modules over (finite dimensional) algebras

66

2.5

Subspace categories and one-point extensions of algebras

82

2.6

Subspace categories of directed vectorspace categories and representations of partially ordered sets

97

Construction of stable separating tubular families

113

3.1

Separating tubular families

113

3.2

Example: Kronecker modules

122

3

3.3

Wing modules

127

3.4

The main theorem

130

3.5

The operation of

3.6

Tame hereditary algebras

153

3.7

Examples: The canonical algebras

161

¢A

on

Ko(A)

149

IV

4

Tilting functors and tubular extensions (notation , results, some proofs)

167

4.1

Tilting modules

167

4.2

Tilted algebras

179

4.3

Concealed algebras

192

4.4

Branches

202

4.5

Ray modules

214

4.6

Tubes

221

4.7

Tubular extensions

230

4.8

Examples: Canonical tubular extensions of canonical algebras

235

4.9

Domestic tubular extensions of tame concealed algebras

241

4.10

The critical directed vectorspace categories and their tubular extensions

254

5

Tubular algebras

268

5.1

Ko(A)

269

5.2

The structure of the module category of a tubular algebra

273

for a tubular and cotubular algebra

5.3

Some