Theorem cbviung

Description: Rule used to change the bound variables in an indexed union, with the substitution specified implicitly by the hypothesis. Usage of this theorem is discouraged because it depends on ax-13 . See cbviun for a version with more disjoint variable conditions, but not requiring ax-13 . (Contributed by NM, 26-Mar-2006) (Revised by Andrew Salmon, 25-Jul-2011) (New usage is discouraged.)

	Ref	Expression
Hypotheses	cbviung.1	|- F/_ y B
	cbviung.2	|- F/_ x C
	cbviung.3	|- ( x = y -> B = C )
Assertion	cbviung	|- U_ x e. A B = U_ y e. A C

Proof

Step	Hyp	Ref	Expression
1		cbviung.1	|- F/_ y B
2		cbviung.2	|- F/_ x C
3		cbviung.3	|- ( x = y -> B = C )
4	1	nfcri	|- F/ y z e. B
5	2	nfcri	|- F/ x z e. C
6	3	eleq2d	|- ( x = y -> ( z e. B <-> z e. C ) )
7	4 5 6	cbvrex	|- ( E. x e. A z e. B <-> E. y e. A z e. C )
8	7	abbii	|- { z | E. x e. A z e. B } = { z | E. y e. A z e. C }
9		df-iun	|- U_ x e. A B = { z | E. x e. A z e. B }
10		df-iun	|- U_ y e. A C = { z | E. y e. A z e. C }
11	8 9 10	3eqtr4i	|- U_ x e. A B = U_ y e. A C