This volume is a revised and enlarged version of Chapters 1 and 2 of a
book with the same title, published in Romanian in 1968. The revision
resulted in a new book which has been divided into two parts because of
the large amount of new material. The present part is intended to
introduce mathematicians and biologists with a strong mathematical and
probabilistic background to the study of stochastic processes. We hope
some readers will be able to discover by themselves the new features of
our treatment such as the inclusion of some unusual topics, the special
attention paid to some usual topics, and the grouping of the material.
We draw the reader's attention to the numbering, because there are
structural differences between the two parts. In Part I there are
Chapters, Sections, Subsections, Paragraphs and Subparagraphs. Thus the
numbering a. b. c. d. e refers to Subparagraph e of Paragraph d of
Subsection c of Section b of Chapter a. Definitions, theorems lemmas and
propositions are numbered a. b. n, n = 1,2, . . ., where a indicates the
chapter and b the section. In Part II there are Sections, Subsections,
Paragraphs, and SUbparagraphs. Thus the numbering a. b. c. d refers to
Subparagraph d of Paragraph c of Subsection b of Section a. Theorems and
lemmas are numbered a. n, n = 1, 2, . . ., where a indicates the
section.