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Mirrors > Home > MPE Home > Th. List > rexdif1en | Structured version Visualization version GIF version |
Description: If a set is equinumerous to a nonzero finite ordinal, then there exists an element in that set such that removing it leaves the set equinumerous to the predecessor of that ordinal. (Contributed by BTernaryTau, 26-Aug-2024.) |
Ref | Expression |
---|---|
rexdif1en | ⊢ ((𝑀 ∈ ω ∧ 𝐴 ≈ suc 𝑀) → ∃𝑥 ∈ 𝐴 (𝐴 ∖ {𝑥}) ≈ 𝑀) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | bren 8541 | . 2 ⊢ (𝐴 ≈ suc 𝑀 ↔ ∃𝑓 𝑓:𝐴–1-1-onto→suc 𝑀) | |
2 | 19.42v 1954 | . . 3 ⊢ (∃𝑓(𝑀 ∈ ω ∧ 𝑓:𝐴–1-1-onto→suc 𝑀) ↔ (𝑀 ∈ ω ∧ ∃𝑓 𝑓:𝐴–1-1-onto→suc 𝑀)) | |
3 | sucidg 6251 | . . . . . 6 ⊢ (𝑀 ∈ ω → 𝑀 ∈ suc 𝑀) | |
4 | f1ocnvdm 7038 | . . . . . . 7 ⊢ ((𝑓:𝐴–1-1-onto→suc 𝑀 ∧ 𝑀 ∈ suc 𝑀) → (◡𝑓‘𝑀) ∈ 𝐴) | |
5 | 4 | ancoms 462 | . . . . . 6 ⊢ ((𝑀 ∈ suc 𝑀 ∧ 𝑓:𝐴–1-1-onto→suc 𝑀) → (◡𝑓‘𝑀) ∈ 𝐴) |
6 | 3, 5 | sylan 583 | . . . . 5 ⊢ ((𝑀 ∈ ω ∧ 𝑓:𝐴–1-1-onto→suc 𝑀) → (◡𝑓‘𝑀) ∈ 𝐴) |
7 | vex 3413 | . . . . . 6 ⊢ 𝑓 ∈ V | |
8 | dif1enlem 8736 | . . . . . 6 ⊢ ((𝑓 ∈ V ∧ 𝑀 ∈ ω ∧ 𝑓:𝐴–1-1-onto→suc 𝑀) → (𝐴 ∖ {(◡𝑓‘𝑀)}) ≈ 𝑀) | |
9 | 7, 8 | mp3an1 1445 | . . . . 5 ⊢ ((𝑀 ∈ ω ∧ 𝑓:𝐴–1-1-onto→suc 𝑀) → (𝐴 ∖ {(◡𝑓‘𝑀)}) ≈ 𝑀) |
10 | sneq 4535 | . . . . . . . 8 ⊢ (𝑥 = (◡𝑓‘𝑀) → {𝑥} = {(◡𝑓‘𝑀)}) | |
11 | 10 | difeq2d 4030 | . . . . . . 7 ⊢ (𝑥 = (◡𝑓‘𝑀) → (𝐴 ∖ {𝑥}) = (𝐴 ∖ {(◡𝑓‘𝑀)})) |
12 | 11 | breq1d 5045 | . . . . . 6 ⊢ (𝑥 = (◡𝑓‘𝑀) → ((𝐴 ∖ {𝑥}) ≈ 𝑀 ↔ (𝐴 ∖ {(◡𝑓‘𝑀)}) ≈ 𝑀)) |
13 | 12 | rspcev 3543 | . . . . 5 ⊢ (((◡𝑓‘𝑀) ∈ 𝐴 ∧ (𝐴 ∖ {(◡𝑓‘𝑀)}) ≈ 𝑀) → ∃𝑥 ∈ 𝐴 (𝐴 ∖ {𝑥}) ≈ 𝑀) |
14 | 6, 9, 13 | syl2anc 587 | . . . 4 ⊢ ((𝑀 ∈ ω ∧ 𝑓:𝐴–1-1-onto→suc 𝑀) → ∃𝑥 ∈ 𝐴 (𝐴 ∖ {𝑥}) ≈ 𝑀) |
15 | 14 | exlimiv 1931 | . . 3 ⊢ (∃𝑓(𝑀 ∈ ω ∧ 𝑓:𝐴–1-1-onto→suc 𝑀) → ∃𝑥 ∈ 𝐴 (𝐴 ∖ {𝑥}) ≈ 𝑀) |
16 | 2, 15 | sylbir 238 | . 2 ⊢ ((𝑀 ∈ ω ∧ ∃𝑓 𝑓:𝐴–1-1-onto→suc 𝑀) → ∃𝑥 ∈ 𝐴 (𝐴 ∖ {𝑥}) ≈ 𝑀) |
17 | 1, 16 | sylan2b 596 | 1 ⊢ ((𝑀 ∈ ω ∧ 𝐴 ≈ suc 𝑀) → ∃𝑥 ∈ 𝐴 (𝐴 ∖ {𝑥}) ≈ 𝑀) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ∧ wa 399 = wceq 1538 ∃wex 1781 ∈ wcel 2111 ∃wrex 3071 Vcvv 3409 ∖ cdif 3857 {csn 4525 class class class wbr 5035 ◡ccnv 5526 suc csuc 6175 –1-1-onto→wf1o 6338 ‘cfv 6339 ωcom 7584 ≈ cen 8529 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1797 ax-4 1811 ax-5 1911 ax-6 1970 ax-7 2015 ax-8 2113 ax-9 2121 ax-10 2142 ax-11 2158 ax-12 2175 ax-ext 2729 ax-sep 5172 ax-nul 5179 ax-pr 5301 ax-un 7464 |
This theorem depends on definitions: df-bi 210 df-an 400 df-or 845 df-3an 1086 df-tru 1541 df-fal 1551 df-ex 1782 df-nf 1786 df-sb 2070 df-mo 2557 df-eu 2588 df-clab 2736 df-cleq 2750 df-clel 2830 df-nfc 2901 df-ne 2952 df-ral 3075 df-rex 3076 df-reu 3077 df-rab 3079 df-v 3411 df-sbc 3699 df-dif 3863 df-un 3865 df-in 3867 df-ss 3877 df-nul 4228 df-if 4424 df-sn 4526 df-pr 4528 df-op 4532 df-uni 4802 df-br 5036 df-opab 5098 df-tr 5142 df-id 5433 df-eprel 5438 df-po 5446 df-so 5447 df-fr 5486 df-we 5488 df-xp 5533 df-rel 5534 df-cnv 5535 df-co 5536 df-dm 5537 df-rn 5538 df-res 5539 df-ima 5540 df-ord 6176 df-on 6177 df-suc 6179 df-iota 6298 df-fun 6341 df-fn 6342 df-f 6343 df-f1 6344 df-fo 6345 df-f1o 6346 df-fv 6347 df-om 7585 df-en 8533 |
This theorem is referenced by: findcard2 8740 |
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