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Mathbox for Jim Kingdon |
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Mirrors > Home > ILE Home > Th. List > Mathboxes > el2oss1o | GIF version |
Description: Being an element of ordinal two implies being a subset of ordinal one. The converse is equivalent to excluded middle by ss1oel2o 13360. (Contributed by Jim Kingdon, 8-Aug-2022.) |
Ref | Expression |
---|---|
el2oss1o | ⊢ (𝐴 ∈ 2o → 𝐴 ⊆ 1o) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | elpri 3555 | . . 3 ⊢ (𝐴 ∈ {∅, 1o} → (𝐴 = ∅ ∨ 𝐴 = 1o)) | |
2 | df2o3 6335 | . . 3 ⊢ 2o = {∅, 1o} | |
3 | 1, 2 | eleq2s 2235 | . 2 ⊢ (𝐴 ∈ 2o → (𝐴 = ∅ ∨ 𝐴 = 1o)) |
4 | 0ss 3406 | . . . 4 ⊢ ∅ ⊆ 1o | |
5 | sseq1 3125 | . . . 4 ⊢ (𝐴 = ∅ → (𝐴 ⊆ 1o ↔ ∅ ⊆ 1o)) | |
6 | 4, 5 | mpbiri 167 | . . 3 ⊢ (𝐴 = ∅ → 𝐴 ⊆ 1o) |
7 | eqimss 3156 | . . 3 ⊢ (𝐴 = 1o → 𝐴 ⊆ 1o) | |
8 | 6, 7 | jaoi 706 | . 2 ⊢ ((𝐴 = ∅ ∨ 𝐴 = 1o) → 𝐴 ⊆ 1o) |
9 | 3, 8 | syl 14 | 1 ⊢ (𝐴 ∈ 2o → 𝐴 ⊆ 1o) |
Colors of variables: wff set class |
Syntax hints: → wi 4 ∨ wo 698 = wceq 1332 ∈ wcel 1481 ⊆ wss 3076 ∅c0 3368 {cpr 3533 1oc1o 6314 2oc2o 6315 |
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 604 ax-in2 605 ax-io 699 ax-5 1424 ax-7 1425 ax-gen 1426 ax-ie1 1470 ax-ie2 1471 ax-8 1483 ax-10 1484 ax-11 1485 ax-i12 1486 ax-bndl 1487 ax-4 1488 ax-17 1507 ax-i9 1511 ax-ial 1515 ax-i5r 1516 ax-ext 2122 |
This theorem depends on definitions: df-bi 116 df-tru 1335 df-nf 1438 df-sb 1737 df-clab 2127 df-cleq 2133 df-clel 2136 df-nfc 2271 df-v 2691 df-dif 3078 df-un 3080 df-in 3082 df-ss 3089 df-nul 3369 df-sn 3538 df-pr 3539 df-suc 4301 df-1o 6321 df-2o 6322 |
This theorem is referenced by: nninfsellemsuc 13383 |
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