Definition df-un 2021

Description: Define the union of two classes. Definition 5.6 of [TakeutiZaring] p. 16. For an alternate definition in terms of class difference, requiring no dummy variables, see dfun2 2214. For union defined in terms of intersection, see dfun3 2217.

Assertion

Ref	Expression
df-un	|- (A u. B) = {x | (x e. A \/ x e. B)}

Distinct variable groups:   x,A   x,B

Detailed syntax breakdown of Definition df-un

Step	Hyp	Ref	Expression
1		cA	. . 3 class A
2		cB	. . 3 class B
3	1, 2	cun 2016	. 2 class (A u. B)
4		vx	. . . . . 6 set x
5	4	cv 1098	. . . . 5 class x
6	5, 1	wcel 1105	. . . 4 wff x e. A
7	5, 2	wcel 1105	. . . 4 wff x e. B
8	6, 7	wo 222	. . 3 wff (x e. A \/ x e. B)
9	8, 4	cab 1440	. 2 class {x | (x e. A \/ x e. B)}
10	3, 9	wceq 1099	1 wff (A u. B) = {x | (x e. A \/ x e. B)}

This definition is referenced by:  elun 2144  ssequn1 2171  unipr 2483  fvclss 3794

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