Blocks of Finite Groups The Hyperfocal Subalgebra of a Block

About 60 years ago, R. Brauer introduced "block theory"; his purpose was to study the group algebra kG of a finite group G over a field k of nonzero characteristic p: any indecomposable two-sided ideal that also is a direct summand of kG determines a G-bl

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Springer-Verlag Berlin Heidelberg GmbH

Lluls Puig ~Jb$Jj- • -!V $

;ff Ftt jf Blocks of

~ #c Finite Groups

#t at.; ~ 1R. ~, -r1\4t

The Hyperfocal Sub algebra of a Block

Springer

Lluis Puig Universite de Paris 7 - Denis Diderot Institut de Mathematiques de Jussieu 175, rue du Chevaleret 75013 Paris, France e-mail: [email protected]

Catalog-in-Publication Data applied for Die Deutsche Bibliotbek - CIP-Einheitsaufnahme Puig, Uufs: Blocks of finite groups: tbe hyperfocal subalgebra of a block /UuisPuig. (Springer monographs in matbematics) ISBN 978-3-662-11256-4 (eBook) ISBN 978-3-642-07802-6 DOI 10.1007/978-3-662-11256-4

Mathematics Subject Classification (2000): 20Cn

ISBN 978-3-642-07802-6

This work is subject to copyright. All rights are reserved, whether the whole or part of tbe material is concerned, specifically tbe rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any otber way, and storage in data banks. Duplication of this publication or parts tbereof is permitted only under the provisions of tbe German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer-Verlag Berlin Heidelberg GmbH. Violations are liable for prosecution under tbe German Copyright Law. http://www.springer.de © Springer-Verlag Berlin Heidelberg 2002 Originally published by Springer-Verlag Berlin Heidelberg New York in 2002 Softcover reprint of the hardcover 1st edition 2002

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4U3142db - 5 4 3 2 1 0 - Printed on acid-free paper

Contents i .................... 1

1. Introduction .......................... 1

2. iJ-~7Gl¥Jf;t1t- .......... 7

2. Lifting Idempotents ................... 7

3.0-1\4fH'-1.S;, *'Al¥J1t4ft ............ 19

3. Points of the O-algebras and Multiplicity of the Points ........ 19

4. N-F9 G-1\4ftJ:.a'-1ft-t .. 31

4. Divisors on N-interior G-algebras .... 31

5. ft-ta'-1 ftl1jil] :f"ft-tl¥Jjj}~ ......... 41

5. Restriction and Induction of Divisors ........................... 41

6. N-F9 G-1\4ftJ:. l¥J A'J-%F A~f ............ 53

6. Local Pointed Groups on N-interior G-algebras ............. 53

7. 10 Green

7. On Green's Indecomposability Theorem .......... 65

1. iJ)

::f!if 7J'- fij'H1. Jt J.'f. . . . . . . 65 8. ~~#N-F9G-1\4ftJl. .. 71 9. G-F91\4ft

Ej N -F9 G-1\ 4ft iJ'J ~

.... 85 10. Xif 1\ 4ftJ:. a'-1 .s;,Xif ........ .

8. Fusions in N-interior G-algebras ..... 71 9. N-interior G-algebras through G-interior AIgebras .......... 85

....................... 99

10. Pointed Groups on the Group Algebra ................ 99

11. G-Jjcl¥J~~Z-1\4ft ... 121

11. Fusion Z-algebra of a Block ......... 121

12. G-Jjca'-1~1\4ft. .