The numbering of formulas, theorems, and statements is its own within every section. When a relation or theorem is cited in the framework of a given section, only its number is indicated, and when a relation or theorem from some other section is cited, that section or subsection is indicated in addition to the number. A number in brackets means a reference to the corresponding number in the list of references. The reference does not mean that the indicated book or article is the only source (or the initial source) of the revelant information. As a rule, definitions are not separated as a special paragraph but are usually entered into the main text. Concepts being defined are given in italics. Elements of the text which are specially emphasized are given in bold face.