Theorem unieq 3818

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 → ∪ 𝐴 = ∪ 𝐵)

Proof of Theorem unieq

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

Step	Hyp	Ref	Expression
1		rexeq 2673	. . 3 ⊢ (𝐴 = 𝐵 → (∃𝑥 ∈ 𝐴 𝑦 ∈ 𝑥 ↔ ∃𝑥 ∈ 𝐵 𝑦 ∈ 𝑥))
2	1	abbidv 2295	. 2 ⊢ (𝐴 = 𝐵 → {𝑦 ∣ ∃𝑥 ∈ 𝐴 𝑦 ∈ 𝑥} = {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 ∈ 𝑥})
3		dfuni2 3811	. 2 ⊢ ∪ 𝐴 = {𝑦 ∣ ∃𝑥 ∈ 𝐴 𝑦 ∈ 𝑥}
4		dfuni2 3811	. 2 ⊢ ∪ 𝐵 = {𝑦 ∣ ∃𝑥 ∈ 𝐵 𝑦 ∈ 𝑥}
5	2, 3, 4	3eqtr4g 2235	1 ⊢ (𝐴 = 𝐵 → ∪ 𝐴 = ∪ 𝐵)

Syntax hints:   → wi 4   = wceq 1353  {cab 2163  ∃wrex 2456  ∪ cuni 3809

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 709  ax-5 1447  ax-7 1448  ax-gen 1449  ax-ie1 1493  ax-ie2 1494  ax-8 1504  ax-10 1505  ax-11 1506  ax-i12 1507  ax-bndl 1509  ax-4 1510  ax-17 1526  ax-i9 1530  ax-ial 1534  ax-i5r 1535  ax-ext 2159

This theorem depends on definitions:  df-bi 117  df-tru 1356  df-nf 1461  df-sb 1763  df-clab 2164  df-cleq 2170  df-clel 2173  df-nfc 2308  df-rex 2461  df-uni 3810

This theorem is referenced by:  unieqi  3819  unieqd  3820  uniintsnr  3880  iununir  3970  treq  4107  limeq  4377  uniex  4437  uniexg  4439  ordsucunielexmid  4530  onsucuni2  4563  nnpredcl  4622  elvvuni  4690  unielrel  5156  unixp0im  5165  iotass  5195  nnsucuniel  6495  en1bg  6799  omp1eom  7093  ctmlemr  7106  nnnninfeq2  7126  uniopn  13392  istopon  13404  eltg3  13450  tgdom  13465  cldval  13492  ntrfval  13493  clsfval  13494  neifval  13533  tgrest  13562  cnprcl2k  13599  bj-uniex  14551  bj-uniexg  14552  nnsf  14636  peano3nninf  14638  exmidsbthr  14653