Minimal Projections in Banach Spaces Problems of Existence and Uniqu

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Wlodzimierz Odyniec Pedagogical University Nab reki Mojki 48 Leningrad 191186, USSR Grzegorz Lewicki Jagiellonian University, Department of Mathematics Reymona 4, 30-059 Krakow, Poland

Mathematics Subject Classification (1980): 41A35, 41A52, 41A65, 46B99, 47A30, 47B05,47B38 ISBN 3-540-53197-1 Springer-Verlag Berlin Heidelberg New York ISBN 0-387-53197-1 Springer-Verlag New York Berlin Heidelberg

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9, 1965, in its current version, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law.

© Springer-Yerlag Berlin Heidelberg 1990 Printed in Germany Printing and binding: Druckhaus Beltz, Hemsbach/Bergstr. 2146/3140-543210 - Printed on acid-free paper

To Marii Schiffmann CElenbogen)

Preface

This book

in

from

Pedagogical

held by

of Bydgoszcz in 1984 - 85.

A

of

I. II. IV) is a revised version of [156J. which appeared in 1985 under copies. in

same

form of mimeographed

(in Russian) in 350

(a

issue).

III includes new The

is

an

Index and

chapter is followed by short

Index; each

on

of

exposed

in the chapter. It is

hope that

book may be of

are just beginining to deepen and approximation

to

wh(

knowledge of Banach space

as well as to specialists. The second chapter

can perhaps prove to be

also

specialists in

economy. This book would never have appeared

encouraging help from

many persons. First of all. the his suggestion

are grateful

Professor Ward Cheney for

submit

and

series and for his inte-

along

Also our

go

Professors Yu.

Konjagin. A. Pelczynski. S. A. Zalgaller. Dr.

way

V. M.

discussions

D. Burago. M.

Rolewicz. P.

Kadec. Dr.

is due

the

version of

Kadec. S.

A. W.

A. Koldobskii and Dr.

problems dealt with in

Special

I. W.

K.

for

book.

Professor Czeslaw Bessaga who has read and helped a

in

final version. Finally. we are glad cikiewicz and Miss J. The

thank Dr.

be able

M.

W6jcikiewicz who

also would like

ran for his help in preparing

E.

Kuczma. Mr M.

W6j'

English.

Dr.

express final version of

M.

Ba-

book on computer.

Wlodzimierz Odyniec and Grzegorz Lewicki Krak6w. April 1990

Table of Contents

1

Introduction §

1. General survey

1

§

2. Terminology and notation

14

Chapter I. Problem of uniqueness of minimal projections

18

in Banach Spaces §

1. Uniqueness of minimal projection with nonunit norm

18

in a three-dimensional Banach space §

2. Certain properties of minimal projections

24

§

3. On the uniqueness or nonuniqueness of minimal projections

32

in the case of dim (B/D) §

2

39

4. Strong uniqueness of minimal projections Notes and remarks

50

Chapter II.