Theorem unieq 3901

Description: Equality theorem for class union. Exercise 15 of [TakeutiZaring] p. 18. (Contributed by NM, 10-Aug-1993.) (Proof shortened by Andrew Salmon, 29-Jun-2011.)

Assertion

Ref	Expression
unieq	|- (A = B -> U.A = U.B)

Proof of Theorem unieq

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

Step	Hyp	Ref	Expression
1		rexeq 2809	. . 3 |- (A = B -> (E.x e. A y e. x <-> E.x e. B y e. x))
2	1	abbidv 2468	. 2 |- (A = B -> {y | E.x e. A y e. x} = {y | E.x e. B y e. x})
3		dfuni2 3894	. 2 |- U.A = {y | E.x e. A y e. x}
4		dfuni2 3894	. 2 |- U.B = {y | E.x e. B y e. x}
5	2, 3, 4	3eqtr4g 2410	1 |- (A = B -> U.A = U.B)

Syntax hints:   -> wi 4   = wceq 1642   e. wcel 1710  {cab 2339  E.wrex 2616  U.cuni 3892

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-17 1616  ax-9 1654  ax-8 1675  ax-6 1729  ax-7 1734  ax-11 1746  ax-12 1925  ax-ext 2334

This theorem depends on definitions:  df-bi 177  df-or 359  df-an 360  df-tru 1319  df-ex 1542  df-nf 1545  df-sb 1649  df-clab 2340  df-cleq 2346  df-clel 2349  df-nfc 2479  df-rex 2621  df-uni 3893

This theorem is referenced by:  unieqi  3902  unieqd  3903  uniintsn  3964  iununi  4051  pw1equn  4332  pw1eqadj  4333  nnadjoin  4521  pw1fnval  5852  pw1fnf1o  5856  brtcfn  6247