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Metamath Proof Explorer

Definition df-xp

Description: Define the Cartesian product of two classes. This is also sometimes called the "cross product" but that term also has other meanings; we intentionally choose a less ambiguous term. Definition 9.11 of Quine p. 64. For example, ( { 1 , 5 } X. { 2 , 7 } ) = ( { <. 1 , 2 >. , <. 1 , 7 >. } u. { <. 5 , 2 >. , <. 5 , 7 >. } ) ( ex-xp ). Another example is that the set of rational numbers is defined in df-q using the Cartesian product ( ZZ X. NN ) ; the left- and right-hand sides of the Cartesian product represent the top (integer) and bottom (natural) numbers of a fraction. (Contributed by NM, 4-Jul-1994)

		Ref	Expression
	Assertion	df-xp	$⊢ A \times B = \{⟨x, y⟩ \| (x \in A \land y \in B)\}$

Detailed syntax breakdown

Step	Hyp	Ref	Expression
0		cA	$class A$
1		cB	$class B$
2	0 1	cxp	$class (A \times B)$
3		vx	$setvar x$
4		vy	$setvar y$
5	3	cv	$setvar x$
6	5 0	wcel	$wff x \in A$
7	4	cv	$setvar y$
8	7 1	wcel	$wff y \in B$
9	6 8	wa	$wff (x \in A \land y \in B)$
10	9 3 4	copab	$class \{⟨x, y⟩ \| (x \in A \land y \in B)\}$
11	2 10	wceq	$wff A \times B = \{⟨x, y⟩ \| (x \in A \land y \in B)\}$