FUNDAMENTALS OF THE THEORY OF OPERATOR ALGEBRAS SPECIATL OPICS VOLUMEI V Advanced Theory-An Exercise Approach This page intentionally left blank FUNDAMENTALS OF THE THEORY OF OPERATOR ALGEBRAS SPECIATLO PICS VOLUMIEV A duanced The0 ry-A n Exercise Approach Richard V. Kadison John R. Ringrose Department of Mathematics School of Mathematics University of Pennsylvania University of Newcastle Philadelphia, Pennsylvania Newcastle upon Tyne, England COPYRIGHT 0 1992, BY RICHARD V. KADISON ALL PARTS RESERVED. NO PART OF THIS PUBLICATION MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM OR BY ANY MEANS, ELEC- TRONIC OR MECHANICAL, INCLUDING PHOTOCOPY, RECORD- ING, OR ANY INFORMATION STORAGE AND RETRIEVAL SYSTEM, WITHOUT PERMISSION IN WRITING FROM RICHARD V. KADISON. THE STATEMENTS OF ALL EXERCISES (0A CADEMIC PRESS 1986) APPEAR WITH THE PERMISSION OF ACADEMIC PRESS. BIRKHAIJSER BOSTON 675 Massachusetts Avenue, Cambridge, MA 02 139-3309 Library of Congress Cataloging-in-Publication Data Kadison, Richard V., 1925- Fundamentals of the theory of operator algebras. (Pure and applied mathematics ; 100-100.2 (QA3.P8 vol. LO)) Vol. 4 has imprint : Boston : Birkhauser. Vol. 3-4: lacks series statement. Includes bibliographies and indexes. Contents: v. 1. Elementary theory -- v. 2. Advanced thcory [etc.] -- v. 4. Special topics : advanced theory, an exercise approach. 1. Operator algebras. I. Ringrose, John R. 11. Title. 111. Series: Pure and applied mathematics (Academic Press) ; 100-100, 2. QA326.K26 1983 512l.55 82-13768 ISBN 0-8176-3498-3 (v. 4) Printed on acid-free paper Printed by Quinn-Woodbine, Woodbine, New Jersey Printed in the U.S.A. ISBN 0-8 176-3498-3 ISBN 3-7643-3498-3 9 8 7 6 5 4 3 2 1 CONTENTS ix Contents of Volume III xi Exercise Groupings Chapter 6. Comparison Theory of Projections 274 - Exercises and Solutions Chapter 7. Normal States and 312 Unitary Equivalence of von Neumann Algebras - Exercises and Solutions Chapter 8. The Trace 368 - Exercises and Solutions Chapter 9. Algebra and Commutant 45 1 - Exercises and Solutions Chapter 10. Special Representations 546 of C*-Algebras - Exercises and Solutions Chapter 11. Tensor Products 680 - Exercises and Solutions Chapter 12. Approximation by Matrix Algebras 726 - Exercises and Solutions Chapter 13. Crossed Products 783 - Exercises and Solutions Chapter 14. Direct Integrals and Decompositions 818 - Exercises and Solutions Bibliography 842 index 847 This page intentionally left blank PREFACE These volumes are companions to the treatise; ‘‘Fundamentals of the Theory of Operator Algebras,” which appeared as Volume 100 - I and I1 in the series, Pure and Applied Mathematics, published by Academic Press in 1983 and 1986, respectively. As stated in the preface to those volumes, “Their primary goal is to teach the sub- ject and lead the reader to the point where the vast recent research literature, both in the subject proper and in its many applications, becomes accessible.” No attempt was made to be encyclopzedic; the choice of material was made from among the fundamentals of what may be called the “classical” theory of operator algebras. By way of supplementing the topics selected for presentation in “Fundamentals,” a substantial list of exercises comprises the last section of each chapter. An equally important purpose of those exer- cises is to develop “hand-on” skills in use of the techniques appearing in the text. As a consequence, each exercise was carefully designed to depend only on the material that precedes it, and separated into segments each of which is realistically capable of solution by an at- tenti ve, diligent, well-mot i vated reader. The process by which the exercises were designed involved solv- ing each of them completely and then subjecting the solutions to detailed scrutiny. It became apparent, in the course of this oper- ation, that the written solutions could be of considerable value, if they were made generally available, as models with which a reader’s solutions could be compared, as indicators of methods and styles for producing further solutions on an individual basis, and as a speedy route through one or another of the many special topics that sup- plement those in the text proper of “Fundamentals” (for the reader without the time or inclination to develop it as an exercise set). The present texts contain those written solutions; the first of these texts has the solutions to the exercises appearing in Volume I of “Fun- damentals” and the second has the solutions to those appearing in Volume 11. The statements of the exercises precede their solutions, for the obvious convenience of the reader. In most instances, where an exercise or group of exercises de- viii P RE FAC E velops a topic, the solutions have been given in what the authors feel is optimal form. Solutions are, of course, geared to the state of knowledge developed at the point in the book where the exer- cise occurs. Very occasionally, this necessitates an approach that is slightly less than optimal (for example, Exercise 2.8.10 occurs before square roots of positive operators, which could be used to advantage in its solution, are introduced). From time to time, an exercise reap- pears, with the task of finding a solution involving newly acquired information. Of course, knowledge of and long experience with the literature of the subject has had a major influence on both the content of the exercises and the form of their solutions. In many cases, there is no specific source for the exercise or its solution. In virtually no instance was the solution of am exercise copied directly from the literature; the solutions were constructed with the path and stage of development of “Fundamentals” where the exercise occurs, very much in mind. Often, where a set of exercises develops a special topic, the solutions present a new and simpler route to the results appearing in the set. References are placed after the solutions. As in “Fundamentals,” no attempt is made to be thorough in referencing. The references appearing are chosen with a few goals in mind: to supply the reader with additional material, closely related to the exercise and its so- lution, that may be of interest for further study, to provide a very sketchy historical context that may be deepened by consulting the papers cited and their bibliographies. Where a set of consecutive exercises is largely inspired by a single article, for the most part, the first of the set and/or the highpoints of the topic note the article. A guide to the topics treated by sets of related exercises follows this preface. CONTENTS OF VOLUME I11 vii Preface ix Contents of Volume iV xi Exercise Groupings Chapter 1. Linear Spaces 1 - Exercises and Solutions Chapter 2. Basics of Hilbert Space and 40 Linear Operators - Exercises and Solutions Chapter 3. Banach Algebras 84 - Exercises and Solutions Chapter 4. Elementary C*-Algebra Theory 139 - Exercises and Solutions Chapter 5. Elementary von Neumann 207 Algebra Theory - Exercises and Solutions Bibliography 263 268 Indez