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Clifford Theory for Group Representations - 1st Edition - ISBN: 9780444873774, 9780080872674

Clifford Theory for Group Representations, Volume 156

1st Edition

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Author: G. Karpilovsky
eBook ISBN: 9780080872674
Imprint: North Holland
Published Date: 1st May 1989
Page Count: 363
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Table of Contents

Preliminaries. Matrix Rings. Artinian, Noetherian and Completely Reducible Modules. The Radical of Modules and Rings. Unique Decompositions. Group Algebras. Cohomology Groups.

Restriction to Normal Subgroups. Induced and Relatively Projective Modules. Restriction of Irreducible Modules to Normal Subgroups. Lifting Idempotents. Restriction of Indecomposable Modules to Normal Subgroups. Similarity with Ground Field Extensions: Preliminary Results, Indecomposable Modules, Irreducible Modules. Restriction of Projective Covers.

Induction and Extension from Normal Subgroups. Group-Graded Algebras and Crossed Products. Graded Ideals. The Endomorphism Ring of Induced Modules. Inducing G-Invariant Modules. Indecomposability of Induced Modules. Homogeneity of Induced Modules. Homogeneity of Induced Modules: An Alternative Approach. The Loewy Length of Induced Modules. Extension from Normal Subgroups: Basic Constructions. Counting Nonisomorphic Extensions. Projective Representations and Inflated Modules. Restriction and Induction of Absolutely Irreducible Modules. Applications: Dimensions of Irreducible Modules and Their Projective Covers. Extensions of Modules over Arbitrary Fields: Projective Crossed Representations, Obstructions to Extensions, The Isaacs-Dade Theorem. Bibliography. Index.


Let N be a normal subgroup of a finite group G and let F be a field. An important method for constructing irreducible FG-modules consists of the application (perhaps repeated) of three basic operations: (i) restriction to FN. (ii) extension from FN. (iii) induction from FN. This is the `Clifford Theory' developed by Clifford in 1937. In the past twenty years, the theory has enjoyed a period of vigorous development. The foundations have been strengthened and reorganized from new points of view, especially from the viewpoint of graded rings and crossed products.

The purpose of this monograph is to tie together various threads of the development in order to give a comprehensive picture of the current state of the subject. It is assumed that the reader has had the equivalent of a standard first-year graduate algebra course, i.e. familiarity with basic ring-theoretic, number-theoretic and group-theoretic concepts, and an understanding of elementary properties of modules, tensor products and fields.


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© North Holland 1989
1st May 1989
North Holland
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About the Author

G. Karpilovsky

Affiliations and Expertise

California State University, Department of Mathematics, Chico, CA, USA