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Theorem ordunidif 5732
 Description: The union of an ordinal stays the same if a subset equal to one of its elements is removed. (Contributed by NM, 10-Dec-2004.)
Assertion
Ref Expression
ordunidif ((Ord 𝐴𝐵𝐴) → (𝐴𝐵) = 𝐴)

Proof of Theorem ordunidif
Dummy variables 𝑥 𝑦 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 ordelon 5706 . . . . . . . 8 ((Ord 𝐴𝐵𝐴) → 𝐵 ∈ On)
2 onelss 5725 . . . . . . . 8 (𝐵 ∈ On → (𝑥𝐵𝑥𝐵))
31, 2syl 17 . . . . . . 7 ((Ord 𝐴𝐵𝐴) → (𝑥𝐵𝑥𝐵))
4 eloni 5692 . . . . . . . . . . 11 (𝐵 ∈ On → Ord 𝐵)
5 ordirr 5700 . . . . . . . . . . 11 (Ord 𝐵 → ¬ 𝐵𝐵)
64, 5syl 17 . . . . . . . . . 10 (𝐵 ∈ On → ¬ 𝐵𝐵)
7 eldif 3565 . . . . . . . . . . 11 (𝐵 ∈ (𝐴𝐵) ↔ (𝐵𝐴 ∧ ¬ 𝐵𝐵))
87simplbi2 654 . . . . . . . . . 10 (𝐵𝐴 → (¬ 𝐵𝐵𝐵 ∈ (𝐴𝐵)))
96, 8syl5 34 . . . . . . . . 9 (𝐵𝐴 → (𝐵 ∈ On → 𝐵 ∈ (𝐴𝐵)))
109adantl 482 . . . . . . . 8 ((Ord 𝐴𝐵𝐴) → (𝐵 ∈ On → 𝐵 ∈ (𝐴𝐵)))
111, 10mpd 15 . . . . . . 7 ((Ord 𝐴𝐵𝐴) → 𝐵 ∈ (𝐴𝐵))
123, 11jctild 565 . . . . . 6 ((Ord 𝐴𝐵𝐴) → (𝑥𝐵 → (𝐵 ∈ (𝐴𝐵) ∧ 𝑥𝐵)))
1312adantr 481 . . . . 5 (((Ord 𝐴𝐵𝐴) ∧ 𝑥𝐴) → (𝑥𝐵 → (𝐵 ∈ (𝐴𝐵) ∧ 𝑥𝐵)))
14 sseq2 3606 . . . . . 6 (𝑦 = 𝐵 → (𝑥𝑦𝑥𝐵))
1514rspcev 3295 . . . . 5 ((𝐵 ∈ (𝐴𝐵) ∧ 𝑥𝐵) → ∃𝑦 ∈ (𝐴𝐵)𝑥𝑦)
1613, 15syl6 35 . . . 4 (((Ord 𝐴𝐵𝐴) ∧ 𝑥𝐴) → (𝑥𝐵 → ∃𝑦 ∈ (𝐴𝐵)𝑥𝑦))
17 eldif 3565 . . . . . . . . 9 (𝑥 ∈ (𝐴𝐵) ↔ (𝑥𝐴 ∧ ¬ 𝑥𝐵))
1817biimpri 218 . . . . . . . 8 ((𝑥𝐴 ∧ ¬ 𝑥𝐵) → 𝑥 ∈ (𝐴𝐵))
19 ssid 3603 . . . . . . . 8 𝑥𝑥
2018, 19jctir 560 . . . . . . 7 ((𝑥𝐴 ∧ ¬ 𝑥𝐵) → (𝑥 ∈ (𝐴𝐵) ∧ 𝑥𝑥))
2120ex 450 . . . . . 6 (𝑥𝐴 → (¬ 𝑥𝐵 → (𝑥 ∈ (𝐴𝐵) ∧ 𝑥𝑥)))
22 sseq2 3606 . . . . . . 7 (𝑦 = 𝑥 → (𝑥𝑦𝑥𝑥))
2322rspcev 3295 . . . . . 6 ((𝑥 ∈ (𝐴𝐵) ∧ 𝑥𝑥) → ∃𝑦 ∈ (𝐴𝐵)𝑥𝑦)
2421, 23syl6 35 . . . . 5 (𝑥𝐴 → (¬ 𝑥𝐵 → ∃𝑦 ∈ (𝐴𝐵)𝑥𝑦))
2524adantl 482 . . . 4 (((Ord 𝐴𝐵𝐴) ∧ 𝑥𝐴) → (¬ 𝑥𝐵 → ∃𝑦 ∈ (𝐴𝐵)𝑥𝑦))
2616, 25pm2.61d 170 . . 3 (((Ord 𝐴𝐵𝐴) ∧ 𝑥𝐴) → ∃𝑦 ∈ (𝐴𝐵)𝑥𝑦)
2726ralrimiva 2960 . 2 ((Ord 𝐴𝐵𝐴) → ∀𝑥𝐴𝑦 ∈ (𝐴𝐵)𝑥𝑦)
28 unidif 4437 . 2 (∀𝑥𝐴𝑦 ∈ (𝐴𝐵)𝑥𝑦 (𝐴𝐵) = 𝐴)
2927, 28syl 17 1 ((Ord 𝐴𝐵𝐴) → (𝐴𝐵) = 𝐴)
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ∧ wa 384   = wceq 1480   ∈ wcel 1987  ∀wral 2907  ∃wrex 2908   ∖ cdif 3552   ⊆ wss 3555  ∪ cuni 4402  Ord word 5681  Oncon0 5682 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1719  ax-4 1734  ax-5 1836  ax-6 1885  ax-7 1932  ax-9 1996  ax-10 2016  ax-11 2031  ax-12 2044  ax-13 2245  ax-ext 2601  ax-sep 4741  ax-nul 4749  ax-pr 4867 This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-3an 1038  df-tru 1483  df-ex 1702  df-nf 1707  df-sb 1878  df-eu 2473  df-mo 2474  df-clab 2608  df-cleq 2614  df-clel 2617  df-nfc 2750  df-ne 2791  df-ral 2912  df-rex 2913  df-rab 2916  df-v 3188  df-sbc 3418  df-dif 3558  df-un 3560  df-in 3562  df-ss 3569  df-nul 3892  df-if 4059  df-sn 4149  df-pr 4151  df-op 4155  df-uni 4403  df-br 4614  df-opab 4674  df-tr 4713  df-eprel 4985  df-po 4995  df-so 4996  df-fr 5033  df-we 5035  df-ord 5685  df-on 5686 This theorem is referenced by: (None)
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