Theorem uniiun 2026

Description: Class union in terms of indexed union. Definition of [Stoll] p. 43.

Assertion

Ref	Expression
uniiun	|- U.A = U.x e. A x

Distinct variable group(s):   x,A

Proof of Theorem uniiun

Step	Hyp	Ref	Expression
1		dfuni2 1921	. 2 |- U.A = {y | E.x e. A y e. x}
2		df-iun 1996	. 2 |- U.x e. A x = {y | E.x e. A y e. x}
3	1, 2	eqtr4 1122	1 |- U.A = U.x e. A x

Syntax hints:   e. wel 803  {cab 1090   = wceq 1091  E.wrex 1202  U.cuni 1919  U.ciun 1994

This theorem is referenced by:  iunpwss 2039  iunpw 2040  oa0r 3141  om1r 3145

This theorem was proved from axioms:  ax-1 3  ax-2 4  ax-3 5  ax-mp 6  ax-4 673  ax-5 674  ax-6 675  ax-7 676  ax-gen 677  ax-8 798  ax-9 799  ax-10 800  ax-11 801  ax-12 802  ax-16 922  ax-17 925  ax-ext 1074

This theorem depends on definitions:  df-bi 128  df-an 198  df-ex 679  df-sb 853  df-clab 1093  df-cleq 1097  df-clel 1099  df-rex 1206  df-uni 1920  df-iun 1996

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