ABSTRACT
The concept of a relation is fundamental in order to understand a broad range of mathematical phenomena. In natural language, relation is understood as correspondence, connection. We say that two objects are related if there is a common property linking them. Defi nition 2.0.1. Consider the sets A and B. We call (binary) relation between the elements of A and B any subset R ¡ A ˆ B. An element a ¢ A is in relation R with an element b ¢ B if and only if (a, b) ¢ R. An element (a, b) ¢ R will be denoted by aRb. D e f i n i t i o n 2 . 0 . 2 . I f A 1, . . . , A n, n ‡ 2 a r e s e t s , w e call an n -ary relation any subset R ¡ A 1 ˆ ˆ An. If n = 2, the relation R is called binary, if n = 3 it is called ternary. If A1 = A2 = . . . = An = A, the relation R is called homogenous.
