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Mirrors > Home > MPE Home > Th. List > onun2 | Structured version Visualization version GIF version |
Description: The union of two ordinals is an ordinal. (Contributed by Scott Fenton, 9-Aug-2024.) |
Ref | Expression |
---|---|
onun2 | ⊢ ((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐴 ∪ 𝐵) ∈ On) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ssequn1 4178 | . . 3 ⊢ (𝐴 ⊆ 𝐵 ↔ (𝐴 ∪ 𝐵) = 𝐵) | |
2 | eleq1a 2829 | . . . 4 ⊢ (𝐵 ∈ On → ((𝐴 ∪ 𝐵) = 𝐵 → (𝐴 ∪ 𝐵) ∈ On)) | |
3 | 2 | adantl 483 | . . 3 ⊢ ((𝐴 ∈ On ∧ 𝐵 ∈ On) → ((𝐴 ∪ 𝐵) = 𝐵 → (𝐴 ∪ 𝐵) ∈ On)) |
4 | 1, 3 | biimtrid 241 | . 2 ⊢ ((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐴 ⊆ 𝐵 → (𝐴 ∪ 𝐵) ∈ On)) |
5 | ssequn2 4181 | . . 3 ⊢ (𝐵 ⊆ 𝐴 ↔ (𝐴 ∪ 𝐵) = 𝐴) | |
6 | eleq1a 2829 | . . . 4 ⊢ (𝐴 ∈ On → ((𝐴 ∪ 𝐵) = 𝐴 → (𝐴 ∪ 𝐵) ∈ On)) | |
7 | 6 | adantr 482 | . . 3 ⊢ ((𝐴 ∈ On ∧ 𝐵 ∈ On) → ((𝐴 ∪ 𝐵) = 𝐴 → (𝐴 ∪ 𝐵) ∈ On)) |
8 | 5, 7 | biimtrid 241 | . 2 ⊢ ((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐵 ⊆ 𝐴 → (𝐴 ∪ 𝐵) ∈ On)) |
9 | eloni 6370 | . . 3 ⊢ (𝐴 ∈ On → Ord 𝐴) | |
10 | eloni 6370 | . . 3 ⊢ (𝐵 ∈ On → Ord 𝐵) | |
11 | ordtri2or2 6459 | . . 3 ⊢ ((Ord 𝐴 ∧ Ord 𝐵) → (𝐴 ⊆ 𝐵 ∨ 𝐵 ⊆ 𝐴)) | |
12 | 9, 10, 11 | syl2an 597 | . 2 ⊢ ((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐴 ⊆ 𝐵 ∨ 𝐵 ⊆ 𝐴)) |
13 | 4, 8, 12 | mpjaod 859 | 1 ⊢ ((𝐴 ∈ On ∧ 𝐵 ∈ On) → (𝐴 ∪ 𝐵) ∈ On) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 397 ∨ wo 846 = wceq 1542 ∈ wcel 2107 ∪ cun 3944 ⊆ wss 3946 Ord word 6359 Oncon0 6360 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1798 ax-4 1812 ax-5 1914 ax-6 1972 ax-7 2012 ax-8 2109 ax-9 2117 ax-ext 2704 ax-sep 5297 ax-nul 5304 ax-pr 5425 |
This theorem depends on definitions: df-bi 206 df-an 398 df-or 847 df-3or 1089 df-3an 1090 df-tru 1545 df-fal 1555 df-ex 1783 df-sb 2069 df-clab 2711 df-cleq 2725 df-clel 2811 df-ne 2942 df-ral 3063 df-rex 3072 df-rab 3434 df-v 3477 df-dif 3949 df-un 3951 df-in 3953 df-ss 3963 df-pss 3965 df-nul 4321 df-if 4527 df-pw 4602 df-sn 4627 df-pr 4629 df-op 4633 df-uni 4907 df-br 5147 df-opab 5209 df-tr 5264 df-eprel 5578 df-po 5586 df-so 5587 df-fr 5629 df-we 5631 df-ord 6363 df-on 6364 |
This theorem is referenced by: onun2i 6482 nosupinfsep 27214 onexlimgt 41924 omabs2 42014 onsucunitp 42055 |
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