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Theorem iununi 4763
Description: A relationship involving union and indexed union. Exercise 25 of [Enderton] p. 33. (Contributed by NM, 25-Nov-2003.) (Proof shortened by Mario Carneiro, 17-Nov-2016.)
Assertion
Ref Expression
iununi ((𝐵 = ∅ → 𝐴 = ∅) ↔ (𝐴 𝐵) = 𝑥𝐵 (𝐴𝑥))
Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Proof of Theorem iununi
StepHypRef Expression
1 df-ne 2934 . . . . . . 7 (𝐵 ≠ ∅ ↔ ¬ 𝐵 = ∅)
2 iunconst 4682 . . . . . . 7 (𝐵 ≠ ∅ → 𝑥𝐵 𝐴 = 𝐴)
31, 2sylbir 225 . . . . . 6 𝐵 = ∅ → 𝑥𝐵 𝐴 = 𝐴)
4 iun0 4729 . . . . . . 7 𝑥𝐵 ∅ = ∅
5 id 22 . . . . . . . 8 (𝐴 = ∅ → 𝐴 = ∅)
65iuneq2d 4700 . . . . . . 7 (𝐴 = ∅ → 𝑥𝐵 𝐴 = 𝑥𝐵 ∅)
74, 6, 53eqtr4a 2821 . . . . . 6 (𝐴 = ∅ → 𝑥𝐵 𝐴 = 𝐴)
83, 7ja 173 . . . . 5 ((𝐵 = ∅ → 𝐴 = ∅) → 𝑥𝐵 𝐴 = 𝐴)
98eqcomd 2767 . . . 4 ((𝐵 = ∅ → 𝐴 = ∅) → 𝐴 = 𝑥𝐵 𝐴)
109uneq1d 3910 . . 3 ((𝐵 = ∅ → 𝐴 = ∅) → (𝐴 𝑥𝐵 𝑥) = ( 𝑥𝐵 𝐴 𝑥𝐵 𝑥))
11 uniiun 4726 . . . 4 𝐵 = 𝑥𝐵 𝑥
1211uneq2i 3908 . . 3 (𝐴 𝐵) = (𝐴 𝑥𝐵 𝑥)
13 iunun 4757 . . 3 𝑥𝐵 (𝐴𝑥) = ( 𝑥𝐵 𝐴 𝑥𝐵 𝑥)
1410, 12, 133eqtr4g 2820 . 2 ((𝐵 = ∅ → 𝐴 = ∅) → (𝐴 𝐵) = 𝑥𝐵 (𝐴𝑥))
15 unieq 4597 . . . . . . 7 (𝐵 = ∅ → 𝐵 = ∅)
16 uni0 4618 . . . . . . 7 ∅ = ∅
1715, 16syl6eq 2811 . . . . . 6 (𝐵 = ∅ → 𝐵 = ∅)
1817uneq2d 3911 . . . . 5 (𝐵 = ∅ → (𝐴 𝐵) = (𝐴 ∪ ∅))
19 un0 4111 . . . . 5 (𝐴 ∪ ∅) = 𝐴
2018, 19syl6eq 2811 . . . 4 (𝐵 = ∅ → (𝐴 𝐵) = 𝐴)
21 iuneq1 4687 . . . . 5 (𝐵 = ∅ → 𝑥𝐵 (𝐴𝑥) = 𝑥 ∈ ∅ (𝐴𝑥))
22 0iun 4730 . . . . 5 𝑥 ∈ ∅ (𝐴𝑥) = ∅
2321, 22syl6eq 2811 . . . 4 (𝐵 = ∅ → 𝑥𝐵 (𝐴𝑥) = ∅)
2420, 23eqeq12d 2776 . . 3 (𝐵 = ∅ → ((𝐴 𝐵) = 𝑥𝐵 (𝐴𝑥) ↔ 𝐴 = ∅))
2524biimpcd 239 . 2 ((𝐴 𝐵) = 𝑥𝐵 (𝐴𝑥) → (𝐵 = ∅ → 𝐴 = ∅))
2614, 25impbii 199 1 ((𝐵 = ∅ → 𝐴 = ∅) ↔ (𝐴 𝐵) = 𝑥𝐵 (𝐴𝑥))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 196   = wceq 1632  wne 2933  cun 3714  c0 4059   cuni 4589   ciun 4673
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1871  ax-4 1886  ax-5 1989  ax-6 2055  ax-7 2091  ax-9 2149  ax-10 2169  ax-11 2184  ax-12 2197  ax-13 2392  ax-ext 2741
This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-tru 1635  df-ex 1854  df-nf 1859  df-sb 2048  df-clab 2748  df-cleq 2754  df-clel 2757  df-nfc 2892  df-ne 2934  df-ral 3056  df-rex 3057  df-v 3343  df-dif 3719  df-un 3721  df-in 3723  df-ss 3730  df-nul 4060  df-sn 4323  df-uni 4590  df-iun 4675
This theorem is referenced by: (None)
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