Theorem unieq 3849

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 2694	. . 3 |- ( A = B -> ( E. x e. A y e. x <-> E. x e. B y e. x ) )
2	1	abbidv 2314	. 2 |- ( A = B -> { y | E. x e. A y e. x } = { y | E. x e. B y e. x } )
3		dfuni2 3842	. 2 |- U. A = { y | E. x e. A y e. x }
4		dfuni2 3842	. 2 |- U. B = { y | E. x e. B y e. x }
5	2, 3, 4	3eqtr4g 2254	1 |- ( A = B -> U. A = U. B )

Syntax hints:   -> wi 4   = wceq 1364   {cab 2182   E.wrex 2476   U.cuni 3840

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 710  ax-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-10 1519  ax-11 1520  ax-i12 1521  ax-bndl 1523  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549  ax-ext 2178

This theorem depends on definitions:  df-bi 117  df-tru 1367  df-nf 1475  df-sb 1777  df-clab 2183  df-cleq 2189  df-clel 2192  df-nfc 2328  df-rex 2481  df-uni 3841

This theorem is referenced by:  unieqi  3850  unieqd  3851  uniintsnr  3911  iununir  4001  treq  4138  limeq  4413  uniex  4473  uniexg  4475  ordsucunielexmid  4568  onsucuni2  4601  nnpredcl  4660  elvvuni  4728  unielrel  5198  unixp0im  5207  iotass  5237  nnsucuniel  6562  en1bg  6868  omp1eom  7170  ctmlemr  7183  nnnninfeq2  7204  uniopn  14321  istopon  14333  eltg3  14377  tgdom  14392  cldval  14419  ntrfval  14420  clsfval  14421  neifval  14460  tgrest  14489  cnprcl2k  14526  bj-uniex  15647  bj-uniexg  15648  nnsf  15736  peano3nninf  15738  exmidsbthr  15754