Introduction

Abstract

The reader may find it more attractive to study selected parts of this book rather than read it page by page. The exposition is organized so as to facilitate the reader’s access to any part which might be of special interest to him. Each chapter begins with an outline (always denoted by 0; thus. e.g. , 3.0 is the outline section of Chapter 3) and each section begins with an introductory note in which we comment briefly on the main notions and results to be found in the section. Again the note is denoted by 0 (thus, e.g. , 3.2.0 is the introductory note of Section 2 of Chapter 3). The outlines and introductory notes should allow the reader to select the things in which he is interested, while providing him with an abbreviated exposition of the parts he may decide to omit.