Theorem uniex 4174

Description: The Axiom of Union in class notation. This says that if A is a set i.e. A e. _V (see isset 2561), 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 3589	. . 3 |- ( x = A -> U. x = U. A )
3	2	eleq1d 2106	. 2 |- ( x = A -> ( U. x e. _V <-> U. A e. _V ) )
4		uniex2 4173	. . 3 |- E. y y = U. x
5	4	issetri 2564	. 2 |- U. x e. _V
6	1, 3, 5	vtocl 2608	1 |- U. A e. _V

Syntax hints:   = wceq 1243   e. wcel 1393   _Vcvv 2557   U.cuni 3580

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-bndl 1399  ax-4 1400  ax-13 1404  ax-14 1405  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428  ax-ext 2022  ax-sep 3875  ax-un 4170

This theorem depends on definitions:  df-bi 110  df-tru 1246  df-nf 1350  df-sb 1646  df-clab 2027  df-cleq 2033  df-clel 2036  df-nfc 2167  df-rex 2312  df-v 2559  df-uni 3581

This theorem is referenced by:  uniexg  4175  unex  4176  uniuni  4183  iunpw  4211  fo1st  5784  fo2nd  5785  brtpos2  5866  tfrexlem  5948  xpcomco  6300  xpassen  6304  pnfnre  7067  pnfxr  8692