Theorem uniex 4420

Description: The Axiom of Union in class notation. This says that if A is a set i.e. A e. _V (see isset 2736), then the union of A is also a set. Same as Axiom 3 of [TakeutiZaring] p. 16. (Contributed by NM, 11-Aug-1993.)

Hypothesis

Ref	Expression
uniex.1	|- A e. _V

Assertion

Ref	Expression
uniex	|- U. A e. _V

Proof of Theorem uniex

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

Step	Hyp	Ref	Expression
1		uniex.1	. 2 |- A e. _V
2		unieq 3803	. . 3 |- ( x = A -> U. x = U. A )
3	2	eleq1d 2239	. 2 |- ( x = A -> ( U. x e. _V <-> U. A e. _V ) )
4		uniex2 4419	. . 3 |- E. y y = U. x
5	4	issetri 2739	. 2 |- U. x e. _V
6	1, 3, 5	vtocl 2784	1 |- U. A e. _V

Syntax hints:   = wceq 1348   e. wcel 2141   _Vcvv 2730   U.cuni 3794

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-13 2143  ax-14 2144  ax-ext 2152  ax-sep 4105  ax-un 4416

This theorem depends on definitions:  df-bi 116  df-tru 1351  df-nf 1454  df-sb 1756  df-clab 2157  df-cleq 2163  df-clel 2166  df-nfc 2301  df-rex 2454  df-v 2732  df-uni 3795

This theorem is referenced by:  vuniex  4421  uniexg  4422  unex  4424  uniuni  4434  iunpw  4463  fo1st  6133  fo2nd  6134  brtpos2  6227  tfrexlem  6310  ixpsnf1o  6710  xpcomco  6800  xpassen  6804  pnfnre  7948  pnfxr  7959