³ A B - C A×B. (a, b) ∈ C, , b a C.
. .
³ . ={1,2,3,4,5} B ={a, b, c, d}, C = {(1,a), (1,d), (2,), (2,d), (3,b), (5,a), (5,b)} A B. 1,2,3,4,5 , a, b, c, d .
ij
C .
. , A, , B. a b , (a, b) .
( ) (A, B, GAB), A, B , , GAB = A×B
()
, C∈A×B . Pr1 C , Pr2C C.
Pr1 C = A, C . .
a∈Pr1 C C b∈Pr2 C, a.
b∈Pr2 C C a∈Pr1 C, b.
A∈Pr1 C, A C ' A. B∈Pr2 C.
³, C A B, D B A , D ={(b, a) | (a, b)∈C}.
³, C, C-1.
, ( ) ,
³,
C ⊆ A×B A B, a ∈Pr1 C Pr2 C.
, , , , : , .
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