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Theorem onsupnmax 43216
Description: If the union of a class of ordinals is not the maximum element of that class, then the union is a limit ordinal or empty. But this isn't a biconditional since 𝐴 could be a non-empty set where a limit ordinal or the empty set happens to be the largest element. (Contributed by RP, 27-Jan-2025.)
Assertion
Ref Expression
onsupnmax (𝐴 ⊆ On → (¬ 𝐴𝐴 𝐴 = 𝐴))

Proof of Theorem onsupnmax
Dummy variables 𝑥 𝑦 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 rexnal 3097 . . . . . . . . 9 (∃𝑥𝐴 ¬ ∃𝑦𝐴 𝑥𝑦 ↔ ¬ ∀𝑥𝐴𝑦𝐴 𝑥𝑦)
2 ralnex 3069 . . . . . . . . . 10 (∀𝑦𝐴 ¬ 𝑥𝑦 ↔ ¬ ∃𝑦𝐴 𝑥𝑦)
32rexbii 3091 . . . . . . . . 9 (∃𝑥𝐴𝑦𝐴 ¬ 𝑥𝑦 ↔ ∃𝑥𝐴 ¬ ∃𝑦𝐴 𝑥𝑦)
4 ssunib 43208 . . . . . . . . . 10 (𝐴 𝐴 ↔ ∀𝑥𝐴𝑦𝐴 𝑥𝑦)
54notbii 320 . . . . . . . . 9 𝐴 𝐴 ↔ ¬ ∀𝑥𝐴𝑦𝐴 𝑥𝑦)
61, 3, 53bitr4ri 304 . . . . . . . 8 𝐴 𝐴 ↔ ∃𝑥𝐴𝑦𝐴 ¬ 𝑥𝑦)
7 simpll 767 . . . . . . . . . . . 12 (((𝐴 ⊆ On ∧ 𝐴 ∈ On) ∧ 𝑥𝐴) → 𝐴 ⊆ On)
87sselda 3994 . . . . . . . . . . 11 ((((𝐴 ⊆ On ∧ 𝐴 ∈ On) ∧ 𝑥𝐴) ∧ 𝑦𝐴) → 𝑦 ∈ On)
9 simpl 482 . . . . . . . . . . . . 13 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → 𝐴 ⊆ On)
109sselda 3994 . . . . . . . . . . . 12 (((𝐴 ⊆ On ∧ 𝐴 ∈ On) ∧ 𝑥𝐴) → 𝑥 ∈ On)
1110adantr 480 . . . . . . . . . . 11 ((((𝐴 ⊆ On ∧ 𝐴 ∈ On) ∧ 𝑥𝐴) ∧ 𝑦𝐴) → 𝑥 ∈ On)
12 ontri1 6419 . . . . . . . . . . 11 ((𝑦 ∈ On ∧ 𝑥 ∈ On) → (𝑦𝑥 ↔ ¬ 𝑥𝑦))
138, 11, 12syl2anc 584 . . . . . . . . . 10 ((((𝐴 ⊆ On ∧ 𝐴 ∈ On) ∧ 𝑥𝐴) ∧ 𝑦𝐴) → (𝑦𝑥 ↔ ¬ 𝑥𝑦))
1413ralbidva 3173 . . . . . . . . 9 (((𝐴 ⊆ On ∧ 𝐴 ∈ On) ∧ 𝑥𝐴) → (∀𝑦𝐴 𝑦𝑥 ↔ ∀𝑦𝐴 ¬ 𝑥𝑦))
1514rexbidva 3174 . . . . . . . 8 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → (∃𝑥𝐴𝑦𝐴 𝑦𝑥 ↔ ∃𝑥𝐴𝑦𝐴 ¬ 𝑥𝑦))
166, 15bitr4id 290 . . . . . . 7 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → (¬ 𝐴 𝐴 ↔ ∃𝑥𝐴𝑦𝐴 𝑦𝑥))
17 unielid 43207 . . . . . . . . 9 ( 𝐴𝐴 ↔ ∃𝑥𝐴𝑦𝐴 𝑦𝑥)
1817a1i 11 . . . . . . . 8 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → ( 𝐴𝐴 ↔ ∃𝑥𝐴𝑦𝐴 𝑦𝑥))
1918biimprd 248 . . . . . . 7 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → (∃𝑥𝐴𝑦𝐴 𝑦𝑥 𝐴𝐴))
2016, 19sylbid 240 . . . . . 6 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → (¬ 𝐴 𝐴 𝐴𝐴))
2120con1d 145 . . . . 5 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → (¬ 𝐴𝐴𝐴 𝐴))
22 uniss 4919 . . . . 5 (𝐴 𝐴 𝐴 𝐴)
2321, 22syl6 35 . . . 4 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → (¬ 𝐴𝐴 𝐴 𝐴))
24 ssorduni 7797 . . . . . . . 8 (𝐴 ⊆ On → Ord 𝐴)
25 orduniss 6482 . . . . . . . 8 (Ord 𝐴 𝐴 𝐴)
2624, 25syl 17 . . . . . . 7 (𝐴 ⊆ On → 𝐴 𝐴)
2726biantrud 531 . . . . . 6 (𝐴 ⊆ On → ( 𝐴 𝐴 ↔ ( 𝐴 𝐴 𝐴 𝐴)))
28 eqss 4010 . . . . . 6 ( 𝐴 = 𝐴 ↔ ( 𝐴 𝐴 𝐴 𝐴))
2927, 28bitr4di 289 . . . . 5 (𝐴 ⊆ On → ( 𝐴 𝐴 𝐴 = 𝐴))
3029adantr 480 . . . 4 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → ( 𝐴 𝐴 𝐴 = 𝐴))
3123, 30sylibd 239 . . 3 ((𝐴 ⊆ On ∧ 𝐴 ∈ On) → (¬ 𝐴𝐴 𝐴 = 𝐴))
3231ex 412 . 2 (𝐴 ⊆ On → ( 𝐴 ∈ On → (¬ 𝐴𝐴 𝐴 = 𝐴)))
33 unon 7850 . . . . 5 On = On
3433a1i 11 . . . 4 ( 𝐴 = On → On = On)
35 unieq 4922 . . . 4 ( 𝐴 = On → 𝐴 = On)
36 id 22 . . . 4 ( 𝐴 = On → 𝐴 = On)
3734, 35, 363eqtr4rd 2785 . . 3 ( 𝐴 = On → 𝐴 = 𝐴)
3837a1i13 27 . 2 (𝐴 ⊆ On → ( 𝐴 = On → (¬ 𝐴𝐴 𝐴 = 𝐴)))
39 ordeleqon 7800 . . 3 (Ord 𝐴 ↔ ( 𝐴 ∈ On ∨ 𝐴 = On))
4024, 39sylib 218 . 2 (𝐴 ⊆ On → ( 𝐴 ∈ On ∨ 𝐴 = On))
4132, 38, 40mpjaod 860 1 (𝐴 ⊆ On → (¬ 𝐴𝐴 𝐴 = 𝐴))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 206  wa 395  wo 847   = wceq 1536  wcel 2105  wral 3058  wrex 3067  wss 3962   cuni 4911  Ord word 6384  Oncon0 6385
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1791  ax-4 1805  ax-5 1907  ax-6 1964  ax-7 2004  ax-8 2107  ax-9 2115  ax-10 2138  ax-11 2154  ax-12 2174  ax-ext 2705  ax-sep 5301  ax-nul 5311  ax-pr 5437  ax-un 7753
This theorem depends on definitions:  df-bi 207  df-an 396  df-or 848  df-3or 1087  df-3an 1088  df-tru 1539  df-fal 1549  df-ex 1776  df-nf 1780  df-sb 2062  df-clab 2712  df-cleq 2726  df-clel 2813  df-ne 2938  df-ral 3059  df-rex 3068  df-rab 3433  df-v 3479  df-dif 3965  df-un 3967  df-in 3969  df-ss 3979  df-pss 3982  df-nul 4339  df-if 4531  df-pw 4606  df-sn 4631  df-pr 4633  df-op 4637  df-uni 4912  df-br 5148  df-opab 5210  df-tr 5265  df-eprel 5588  df-po 5596  df-so 5597  df-fr 5640  df-we 5642  df-ord 6388  df-on 6389  df-suc 6391
This theorem is referenced by:  onsupeqnmax  43235  onsupsucismax  43268
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