Theorem dfuni2 4438

Description: Alternate definition of class union. (Contributed by NM, 28-Jun-1998.)

Assertion

Ref	Expression
dfuni2	|- U. A = { x | E. y e. A x e. y }

Distinct variable group:   x, y, A

Proof of Theorem dfuni2

Step	Hyp	Ref	Expression
1		df-uni 4437	. 2 |- U. A = { x | E. y ( x e. y /\ y e. A ) }
2		exancom 1787	. . . 4 |- ( E. y ( x e. y /\ y e. A ) <-> E. y ( y e. A /\ x e. y ) )
3		df-rex 2918	. . . 4 |- ( E. y e. A x e. y <-> E. y ( y e. A /\ x e. y ) )
4	2, 3	bitr4i 267	. . 3 |- ( E. y ( x e. y /\ y e. A ) <-> E. y e. A x e. y )
5	4	abbii 2739	. 2 |- { x | E. y ( x e. y /\ y e. A ) } = { x | E. y e. A x e. y }
6	1, 5	eqtri 2644	1 |- U. A = { x | E. y e. A x e. y }

Syntax hints:   /\ wa 384   = wceq 1483   E.wex 1704   e. wcel 1990   {cab 2608   E.wrex 2913   U.cuni 4436

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1722  ax-4 1737  ax-5 1839  ax-6 1888  ax-7 1935  ax-9 1999  ax-10 2019  ax-11 2034  ax-12 2047  ax-13 2246  ax-ext 2602

This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1486  df-ex 1705  df-nf 1710  df-sb 1881  df-clab 2609  df-cleq 2615  df-clel 2618  df-rex 2918  df-uni 4437

This theorem is referenced by:  nfuni  4442  nfunid  4443  unieq  4444  uniiun  4573  rncnvepres  34073