Theorem unipr 4225

Description: The union of a pair is the union of its members. Proposition 5.7 of [TakeutiZaring] p. 16. (Contributed by NM, 23-Aug-1993.)

Hypotheses

Ref	Expression
unipr.1	|- A e. _V
unipr.2	|- B e. _V

Assertion

Ref	Expression
unipr	|- U. { A , B } = ( A u. B )

Proof of Theorem unipr

Dummy variables x y are mutually distinct and distinct from all other variables.

Step	Hyp	Ref	Expression
1		19.43 1756	. . . 4 |- ( E. y ( ( x e. y /\ y = A ) \/ ( x e. y /\ y = B ) ) <-> ( E. y ( x e. y /\ y = A ) \/ E. y ( x e. y /\ y = B ) ) )
2		vex 3060	. . . . . . . 8 |- y e. _V
3	2	elpr 3998	. . . . . . 7 |- ( y e. { A , B } <-> ( y = A \/ y = B ) )
4	3	anbi2i 705	. . . . . 6 |- ( ( x e. y /\ y e. { A , B } ) <-> ( x e. y /\ ( y = A \/ y = B ) ) )
5		andi 883	. . . . . 6 |- ( ( x e. y /\ ( y = A \/ y = B ) ) <-> ( ( x e. y /\ y = A ) \/ ( x e. y /\ y = B ) ) )
6	4, 5	bitri 257	. . . . 5 |- ( ( x e. y /\ y e. { A , B } ) <-> ( ( x e. y /\ y = A ) \/ ( x e. y /\ y = B ) ) )
7	6	exbii 1729	. . . 4 |- ( E. y ( x e. y /\ y e. { A , B } ) <-> E. y ( ( x e. y /\ y = A ) \/ ( x e. y /\ y = B ) ) )
8		unipr.1	. . . . . . 7 |- A e. _V
9	8	clel3 3189	. . . . . 6 |- ( x e. A <-> E. y ( y = A /\ x e. y ) )
10		exancom 1733	. . . . . 6 |- ( E. y ( y = A /\ x e. y ) <-> E. y ( x e. y /\ y = A ) )
11	9, 10	bitri 257	. . . . 5 |- ( x e. A <-> E. y ( x e. y /\ y = A ) )
12		unipr.2	. . . . . . 7 |- B e. _V
13	12	clel3 3189	. . . . . 6 |- ( x e. B <-> E. y ( y = B /\ x e. y ) )
14		exancom 1733	. . . . . 6 |- ( E. y ( y = B /\ x e. y ) <-> E. y ( x e. y /\ y = B ) )
15	13, 14	bitri 257	. . . . 5 |- ( x e. B <-> E. y ( x e. y /\ y = B ) )
16	11, 15	orbi12i 528	. . . 4 |- ( ( x e. A \/ x e. B ) <-> ( E. y ( x e. y /\ y = A ) \/ E. y ( x e. y /\ y = B ) ) )
17	1, 7, 16	3bitr4ri 286	. . 3 |- ( ( x e. A \/ x e. B ) <-> E. y ( x e. y /\ y e. { A , B } ) )
18	17	abbii 2578	. 2 |- { x | ( x e. A \/ x e. B ) } = { x | E. y ( x e. y /\ y e. { A , B } ) }
19		df-un 3421	. 2 |- ( A u. B ) = { x | ( x e. A \/ x e. B ) }
20		df-uni 4213	. 2 |- U. { A , B } = { x | E. y ( x e. y /\ y e. { A , B } ) }
21	18, 19, 20	3eqtr4ri 2495	1 |- U. { A , B } = ( A u. B )

Syntax hints:   \/ wo 374   /\ wa 375   = wceq 1455   E.wex 1674   e. wcel 1898   {cab 2448   _Vcvv 3057   u. cun 3414   {cpr 3982   U.cuni 4212

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1680  ax-4 1693  ax-5 1769  ax-6 1816  ax-7 1862  ax-10 1926  ax-11 1931  ax-12 1944  ax-13 2102  ax-ext 2442

This theorem depends on definitions:  df-bi 190  df-or 376  df-an 377  df-tru 1458  df-ex 1675  df-nf 1679  df-sb 1809  df-clab 2449  df-cleq 2455  df-clel 2458  df-nfc 2592  df-v 3059  df-un 3421  df-sn 3981  df-pr 3983  df-uni 4213

This theorem is referenced by:  uniprg  4226  unisn  4227  uniintsn  4286  uniop  4718  unex  6616  rankxplim  8376  mrcun  15577  indistps  20075  indistps2  20076  leordtval2  20277  ex-uni  25925  fouriersw  38133