Theorem unjust 3074

Description: Soundness justification theorem for df-un 3075. (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 2202	. . . 4 |- ( x = z -> ( x e. A <-> z e. A ) )
2		eleq1 2202	. . . 4 |- ( x = z -> ( x e. B <-> z e. B ) )
3	1, 2	orbi12d 782	. . 3 |- ( x = z -> ( ( x e. A \/ x e. B ) <-> ( z e. A \/ z e. B ) ) )
4	3	cbvabv 2264	. 2 |- { x | ( x e. A \/ x e. B ) } = { z | ( z e. A \/ z e. B ) }
5		eleq1 2202	. . . 4 |- ( z = y -> ( z e. A <-> y e. A ) )
6		eleq1 2202	. . . 4 |- ( z = y -> ( z e. B <-> y e. B ) )
7	5, 6	orbi12d 782	. . 3 |- ( z = y -> ( ( z e. A \/ z e. B ) <-> ( y e. A \/ y e. B ) ) )
8	7	cbvabv 2264	. 2 |- { z | ( z e. A \/ z e. B ) } = { y | ( y e. A \/ y e. B ) }
9	4, 8	eqtri 2160	1 |- { x | ( x e. A \/ x e. B ) } = { y | ( y e. A \/ y e. B ) }

Syntax hints:   \/ wo 697   = wceq 1331   e. wcel 1480   {cab 2125

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 698  ax-5 1423  ax-7 1424  ax-gen 1425  ax-ie1 1469  ax-ie2 1470  ax-8 1482  ax-10 1483  ax-11 1484  ax-i12 1485  ax-bndl 1486  ax-4 1487  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2121

This theorem depends on definitions:  df-bi 116  df-nf 1437  df-sb 1736  df-clab 2126  df-cleq 2132  df-clel 2135

This theorem is referenced by: (None)