The book is based on lectures repeatedly given by the authors to students of MGZPI. A rotaprint version of this book was previously published. The theoretical part of this manual was written by N.Ya. Vilenkin and V.V. Zuckerman. Exercises compiled by M.A. Dobrokhotova, A.N. Safonov and V.V. Zuckerman. The book is divided into chapters, paragraphs and paragraphs. The numbering of theorems, lemmas, examples and formulas is continuous within each paragraph. Almost all paragraphs are equipped with exercises and self-test questions.