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Metamath Proof Explorer

Definition df-dm

Description: Define the domain of a class. Definition 3 of Suppes p. 59. For example, F = { <. 2 , 6 >. , <. 3 , 9 >. } -> dom F = { 2 , 3 } ( ex-dm ). Another example is the domain of the complex arctangent, ( A e. dom arctan <-> ( A e. CC /\ A =/= -ui /\ A =/= i ) ) (for proof see atandm ). Contrast with range (defined in df-rn ). For alternate definitions see dfdm2 , dfdm3 , and dfdm4 . The notation " dom " is used by Enderton; other authors sometimes use script D. (Contributed by NM, 1-Aug-1994)

		Ref	Expression
	Assertion	df-dm	$⊢ dom A = \{x \| \exists y x A y\}$

Detailed syntax breakdown

Step	Hyp	Ref	Expression
0		cA	$class A$
1	0	cdm	$class dom A$
2		vx	$setvar x$
3		vy	$setvar y$
4	2	cv	$setvar x$
5	3	cv	$setvar y$
6	4 5 0	wbr	$wff x A y$
7	6 3	wex	$wff \exists y x A y$
8	7 2	cab	$class \{x \| \exists y x A y\}$
9	1 8	wceq	$wff dom A = \{x \| \exists y x A y\}$