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Mirrors > Home > MPE Home > Th. List > en2 | Structured version Visualization version GIF version |
Description: A set equinumerous to ordinal 2 is a pair. (Contributed by Mario Carneiro, 5-Jan-2016.) |
Ref | Expression |
---|---|
en2 | ⊢ (𝐴 ≈ 2o → ∃𝑥∃𝑦 𝐴 = {𝑥, 𝑦}) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 1on 8517 | . . 3 ⊢ 1o ∈ On | |
2 | 1 | onordi 6497 | . 2 ⊢ Ord 1o |
3 | df-2o 8506 | . 2 ⊢ 2o = suc 1o | |
4 | en1 9063 | . . 3 ⊢ ((𝐴 ∖ {𝑥}) ≈ 1o ↔ ∃𝑦(𝐴 ∖ {𝑥}) = {𝑦}) | |
5 | 4 | biimpi 216 | . 2 ⊢ ((𝐴 ∖ {𝑥}) ≈ 1o → ∃𝑦(𝐴 ∖ {𝑥}) = {𝑦}) |
6 | df-pr 4634 | . . . 4 ⊢ {𝑥, 𝑦} = ({𝑥} ∪ {𝑦}) | |
7 | 6 | enp1ilem 9310 | . . 3 ⊢ (𝑥 ∈ 𝐴 → ((𝐴 ∖ {𝑥}) = {𝑦} → 𝐴 = {𝑥, 𝑦})) |
8 | 7 | eximdv 1915 | . 2 ⊢ (𝑥 ∈ 𝐴 → (∃𝑦(𝐴 ∖ {𝑥}) = {𝑦} → ∃𝑦 𝐴 = {𝑥, 𝑦})) |
9 | 2, 3, 5, 8 | enp1i 9311 | 1 ⊢ (𝐴 ≈ 2o → ∃𝑥∃𝑦 𝐴 = {𝑥, 𝑦}) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 = wceq 1537 ∃wex 1776 ∈ wcel 2106 ∖ cdif 3960 {csn 4631 {cpr 4633 class class class wbr 5148 1oc1o 8498 2oc2o 8499 ≈ cen 8981 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1792 ax-4 1806 ax-5 1908 ax-6 1965 ax-7 2005 ax-8 2108 ax-9 2116 ax-10 2139 ax-11 2155 ax-12 2175 ax-ext 2706 ax-sep 5302 ax-nul 5312 ax-pr 5438 |
This theorem depends on definitions: df-bi 207 df-an 396 df-or 848 df-3or 1087 df-3an 1088 df-tru 1540 df-fal 1550 df-ex 1777 df-nf 1781 df-sb 2063 df-mo 2538 df-eu 2567 df-clab 2713 df-cleq 2727 df-clel 2814 df-ne 2939 df-ral 3060 df-rex 3069 df-reu 3379 df-rab 3434 df-v 3480 df-dif 3966 df-un 3968 df-in 3970 df-ss 3980 df-pss 3983 df-nul 4340 df-if 4532 df-pw 4607 df-sn 4632 df-pr 4634 df-op 4638 df-uni 4913 df-br 5149 df-opab 5211 df-tr 5266 df-id 5583 df-eprel 5589 df-po 5597 df-so 5598 df-fr 5641 df-we 5643 df-xp 5695 df-rel 5696 df-cnv 5697 df-co 5698 df-dm 5699 df-rn 5700 df-res 5701 df-ima 5702 df-ord 6389 df-on 6390 df-suc 6392 df-iota 6516 df-fun 6565 df-fn 6566 df-f 6567 df-f1 6568 df-fo 6569 df-f1o 6570 df-fv 6571 df-1o 8505 df-2o 8506 df-en 8985 |
This theorem is referenced by: en3 9314 hash2pr 14505 pmtrrn2 19493 trsp2cyc 33126 en2pr 43537 pr2cv 43538 |
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