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Mirrors > Home > ILE Home > Th. List > elnn | GIF version |
Description: A member of a natural number is a natural number. (Contributed by NM, 21-Jun-1998.) |
Ref | Expression |
---|---|
elnn | ⊢ ((𝐴 ∈ 𝐵 ∧ 𝐵 ∈ ω) → 𝐴 ∈ ω) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | sseq1 3120 | . . 3 ⊢ (𝑦 = ∅ → (𝑦 ⊆ ω ↔ ∅ ⊆ ω)) | |
2 | sseq1 3120 | . . 3 ⊢ (𝑦 = 𝑥 → (𝑦 ⊆ ω ↔ 𝑥 ⊆ ω)) | |
3 | sseq1 3120 | . . 3 ⊢ (𝑦 = suc 𝑥 → (𝑦 ⊆ ω ↔ suc 𝑥 ⊆ ω)) | |
4 | sseq1 3120 | . . 3 ⊢ (𝑦 = 𝐵 → (𝑦 ⊆ ω ↔ 𝐵 ⊆ ω)) | |
5 | 0ss 3401 | . . 3 ⊢ ∅ ⊆ ω | |
6 | unss 3250 | . . . . . 6 ⊢ ((𝑥 ⊆ ω ∧ {𝑥} ⊆ ω) ↔ (𝑥 ∪ {𝑥}) ⊆ ω) | |
7 | vex 2689 | . . . . . . . 8 ⊢ 𝑥 ∈ V | |
8 | 7 | snss 3649 | . . . . . . 7 ⊢ (𝑥 ∈ ω ↔ {𝑥} ⊆ ω) |
9 | 8 | anbi2i 452 | . . . . . 6 ⊢ ((𝑥 ⊆ ω ∧ 𝑥 ∈ ω) ↔ (𝑥 ⊆ ω ∧ {𝑥} ⊆ ω)) |
10 | df-suc 4293 | . . . . . . 7 ⊢ suc 𝑥 = (𝑥 ∪ {𝑥}) | |
11 | 10 | sseq1i 3123 | . . . . . 6 ⊢ (suc 𝑥 ⊆ ω ↔ (𝑥 ∪ {𝑥}) ⊆ ω) |
12 | 6, 9, 11 | 3bitr4i 211 | . . . . 5 ⊢ ((𝑥 ⊆ ω ∧ 𝑥 ∈ ω) ↔ suc 𝑥 ⊆ ω) |
13 | 12 | biimpi 119 | . . . 4 ⊢ ((𝑥 ⊆ ω ∧ 𝑥 ∈ ω) → suc 𝑥 ⊆ ω) |
14 | 13 | expcom 115 | . . 3 ⊢ (𝑥 ∈ ω → (𝑥 ⊆ ω → suc 𝑥 ⊆ ω)) |
15 | 1, 2, 3, 4, 5, 14 | finds 4514 | . 2 ⊢ (𝐵 ∈ ω → 𝐵 ⊆ ω) |
16 | ssel2 3092 | . . 3 ⊢ ((𝐵 ⊆ ω ∧ 𝐴 ∈ 𝐵) → 𝐴 ∈ ω) | |
17 | 16 | ancoms 266 | . 2 ⊢ ((𝐴 ∈ 𝐵 ∧ 𝐵 ⊆ ω) → 𝐴 ∈ ω) |
18 | 15, 17 | sylan2 284 | 1 ⊢ ((𝐴 ∈ 𝐵 ∧ 𝐵 ∈ ω) → 𝐴 ∈ ω) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∧ wa 103 ∈ wcel 1480 ∪ cun 3069 ⊆ wss 3071 ∅c0 3363 {csn 3527 suc csuc 4287 ωcom 4504 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia1 105 ax-ia2 106 ax-ia3 107 ax-in1 603 ax-in2 604 ax-io 698 ax-5 1423 ax-7 1424 ax-gen 1425 ax-ie1 1469 ax-ie2 1470 ax-8 1482 ax-10 1483 ax-11 1484 ax-i12 1485 ax-bndl 1486 ax-4 1487 ax-13 1491 ax-14 1492 ax-17 1506 ax-i9 1510 ax-ial 1514 ax-i5r 1515 ax-ext 2121 ax-sep 4046 ax-nul 4054 ax-pow 4098 ax-pr 4131 ax-un 4355 ax-iinf 4502 |
This theorem depends on definitions: df-bi 116 df-3an 964 df-tru 1334 df-nf 1437 df-sb 1736 df-clab 2126 df-cleq 2132 df-clel 2135 df-nfc 2270 df-ral 2421 df-rex 2422 df-v 2688 df-dif 3073 df-un 3075 df-in 3077 df-ss 3084 df-nul 3364 df-pw 3512 df-sn 3533 df-pr 3534 df-uni 3737 df-int 3772 df-suc 4293 df-iom 4505 |
This theorem is referenced by: ordom 4520 peano2b 4528 nntr2 6399 nndifsnid 6403 nnaordi 6404 nnmordi 6412 fidceq 6763 nnwetri 6804 enumctlemm 6999 ennnfonelemdm 11933 ennnfonelemnn0 11935 nnti 13191 nninfsellemdc 13206 nninfsellemeq 13210 nninfsellemeqinf 13212 |
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