615 B
615 B
Page 512
Definition
Let R be a relation from A to B. Define the inverse relation R^{-1} from
B to A as follows:
R^{-1} = \{(y, x) \in B \times A | (x, y) \in R\} Page 513
Definition
A relation on a set A is a relation from A to A.
Page 514
Definition
Given sets A_1, A_2, \dots, A_n an $n$-ary relation R on
A_1 \times A_2 \times \cdots \times A_n is a subset of
A_1 \times A_2 \times \cdots \times A_n. The special cases of $2$-ary,
$3$-ary, and $4$-ary relations are called binary, ternary, and
quarternary relations, respectively.