Rings and Modules of Quotients

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237 80 Stenstrom University of Stockholm, Stockholm/Sweden

Rings and Modules of Quotients

,· t ,

.

Springer-Verlag Berlin· Heidelberg· NewYork 1971

Lecture Notes in Mathematics A collection of informal reports and seminars Edited by A. Dold, Heidelberg and B. Eckmann, ZOrich

237 80 Stenstrom University of Stockholm, Stockholm/Sweden

Rings and Modules of Quotients

,· t ,

.

Springer-Verlag Berlin· Heidelberg· NewYork 1971

AMS Subject Classifications (1970): 16A 08

ISBN 3-540-05690-4 Springer-Verlag Berlin . Heidelberg . New York ISBN 0-387-05690-4 Springer-Verlag New York· Heidelberg· Berlin 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 the publisher, the amount of the fee to be determined by agreement with the publisher. @ by Springer-Verlag Berlin' Heidelberg 1971. Library of Congress Catalog Card Number 70-180692. Printed in Germany.

Offsetdruck: Julius Beltz, Hemsbach

Contents

Chapter 1. Torsion theory 1.

Preradioals

1

2.

Torsion theories

4

3.

Topologies

12

4. 5. 6.

Stable torsion theories

20

Topologies for a oommutative noetherian ring

23

!-injective modules

29

Chapter 2. Categories of modules of quotients 7.

Construction of rings and modules of quotients

8.

Modules of quotients and !-injective envelopes

41

9.

Coreflective suboategories of

44

10.

Giraud subcategories and the Popescu-Gabriel

Mod-A

theorem

33

48

Chapter 3. General properties of rings of quotients 11.

Lattioes of !-pure submodules

58

12.

Finiteness oonditions on topologies

68

13.

Flat epimorphisms of rings

12

14.

Maximal flat epimorphic extension of a ring

82

15.

I-topologies and rings of fractions

86

Chapter 4. Se1f-injeotive rings 16.

The endomorphism ring of an injeotive module

93

17.

Coperfect rings

91

18.

Quasi-Frobenius rings

101

Chapter 5. Maximal and classical rings of quotients 19.

The maximal ring of quotients

20.

The maximal ring of quotients of a non-singular ring

110 113

21.

The maximal ring of quotients of a reduced ring

118

22.

The olassioal ring of quotients

123

References

130

Introduction These notes are intended to give a survey 01 the basic, more or less well-known, results in the theory of rings of quotients.

An effort has been made to make the account as self-contained and elementary as possible. Thus we assume from the reader only a knowledge of the elements of the theory of rings and of abelian categories. We will briefly describe the contents of the notes. Chapter 1 treats the necessary preliminaries on torsion theory. The main result here is the establishing of a 1-1 correspondence between hereditary torsion theories and topologies on a ring (Gabriel [31] and Maranda

(51]).

Tn Chapter 2 we constr