Theorem unjust 3124

Description: Soundness justification theorem for df-un 3125. (Contributed by Rodolfo Medina, 28-Apr-2010.) (Proof shortened by Andrew Salmon, 9-Jul-2011.)

Assertion

Ref	Expression
unjust	|- { x | ( x e. A \/ x e. B ) } = { y | ( y e. A \/ y e. B ) }

Distinct variable groups:   x, A   x, B   y, A   y, B

Proof of Theorem unjust

Dummy variable z is distinct from all other variables.

Step	Hyp	Ref	Expression
1		eleq1 2233	. . . 4 |- ( x = z -> ( x e. A <-> z e. A ) )
2		eleq1 2233	. . . 4 |- ( x = z -> ( x e. B <-> z e. B ) )
3	1, 2	orbi12d 788	. . 3 |- ( x = z -> ( ( x e. A \/ x e. B ) <-> ( z e. A \/ z e. B ) ) )
4	3	cbvabv 2295	. 2 |- { x | ( x e. A \/ x e. B ) } = { z | ( z e. A \/ z e. B ) }
5		eleq1 2233	. . . 4 |- ( z = y -> ( z e. A <-> y e. A ) )
6		eleq1 2233	. . . 4 |- ( z = y -> ( z e. B <-> y e. B ) )
7	5, 6	orbi12d 788	. . 3 |- ( z = y -> ( ( z e. A \/ z e. B ) <-> ( y e. A \/ y e. B ) ) )
8	7	cbvabv 2295	. 2 |- { z | ( z e. A \/ z e. B ) } = { y | ( y e. A \/ y e. B ) }
9	4, 8	eqtri 2191	1 |- { x | ( x e. A \/ x e. B ) } = { y | ( y e. A \/ y e. B ) }

Syntax hints:   \/ wo 703   = wceq 1348   e. wcel 2141   {cab 2156

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-io 704  ax-5 1440  ax-7 1441  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-8 1497  ax-10 1498  ax-11 1499  ax-i12 1500  ax-bndl 1502  ax-4 1503  ax-17 1519  ax-i9 1523  ax-ial 1527  ax-i5r 1528  ax-ext 2152

This theorem depends on definitions:  df-bi 116  df-nf 1454  df-sb 1756  df-clab 2157  df-cleq 2163  df-clel 2166

This theorem is referenced by: (None)