This book is divided into six chapters, and each chapter is subdivided into a certain number of sections. Formulas that are used again at some later point are numbered sectionwise in parentheses: (1). When referring to formula (5) of the current section, we do not give the section number; 3.4.(2), however, denotes formula (2) of Section 3.4.

New terms are printed in slanted type at their place of definition or first appearance; as a rule there is no further warning of the "Watch out: Here comes a definition!" type. The exact spot where a term is defined is referenced in the index at the back of the book.

Propositions and theorems are numbered by chapters, the boldface marker (4.3) denoting the third theorem in Chapter 4. Theorems are usually announced; in any case they are recognizable from the marker at the beginning and from their text being printed in slanted type. The two corners ? and ? denote the beginning and the end of a proof.

Circled numbers ? mark the beginning of examples, some of them of a more explanatory nature, some of them describing famous animals created by means of the general theory. The numbering of examples begins anew in each section; the empty circle ? marks the end of an example.

A family of objects c _? over the index set I (called an array for short) is designated by

1 _A denotes the characteristic function...