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Mirrors > Home > MPE Home > Th. List > card1 | Structured version Visualization version GIF version |
Description: A set has cardinality one iff it is a singleton. (Contributed by Mario Carneiro, 10-Jan-2013.) |
Ref | Expression |
---|---|
card1 | ⊢ ((card‘𝐴) = 1o ↔ ∃𝑥 𝐴 = {𝑥}) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | 1onn 8254 | . . . . . . . 8 ⊢ 1o ∈ ω | |
2 | cardnn 9380 | . . . . . . . 8 ⊢ (1o ∈ ω → (card‘1o) = 1o) | |
3 | 1, 2 | ax-mp 5 | . . . . . . 7 ⊢ (card‘1o) = 1o |
4 | 1n0 8108 | . . . . . . 7 ⊢ 1o ≠ ∅ | |
5 | 3, 4 | eqnetri 3083 | . . . . . 6 ⊢ (card‘1o) ≠ ∅ |
6 | carden2a 9383 | . . . . . 6 ⊢ (((card‘1o) = (card‘𝐴) ∧ (card‘1o) ≠ ∅) → 1o ≈ 𝐴) | |
7 | 5, 6 | mpan2 687 | . . . . 5 ⊢ ((card‘1o) = (card‘𝐴) → 1o ≈ 𝐴) |
8 | 7 | eqcoms 2826 | . . . 4 ⊢ ((card‘𝐴) = (card‘1o) → 1o ≈ 𝐴) |
9 | 8 | ensymd 8548 | . . 3 ⊢ ((card‘𝐴) = (card‘1o) → 𝐴 ≈ 1o) |
10 | carden2b 9384 | . . 3 ⊢ (𝐴 ≈ 1o → (card‘𝐴) = (card‘1o)) | |
11 | 9, 10 | impbii 210 | . 2 ⊢ ((card‘𝐴) = (card‘1o) ↔ 𝐴 ≈ 1o) |
12 | 3 | eqeq2i 2831 | . 2 ⊢ ((card‘𝐴) = (card‘1o) ↔ (card‘𝐴) = 1o) |
13 | en1 8564 | . 2 ⊢ (𝐴 ≈ 1o ↔ ∃𝑥 𝐴 = {𝑥}) | |
14 | 11, 12, 13 | 3bitr3i 302 | 1 ⊢ ((card‘𝐴) = 1o ↔ ∃𝑥 𝐴 = {𝑥}) |
Colors of variables: wff setvar class |
Syntax hints: ↔ wb 207 = wceq 1528 ∃wex 1771 ∈ wcel 2105 ≠ wne 3013 ∅c0 4288 {csn 4557 class class class wbr 5057 ‘cfv 6348 ωcom 7569 1oc1o 8084 ≈ cen 8494 cardccrd 9352 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1787 ax-4 1801 ax-5 1902 ax-6 1961 ax-7 2006 ax-8 2107 ax-9 2115 ax-10 2136 ax-11 2151 ax-12 2167 ax-ext 2790 ax-sep 5194 ax-nul 5201 ax-pow 5257 ax-pr 5320 ax-un 7450 |
This theorem depends on definitions: df-bi 208 df-an 397 df-or 842 df-3or 1080 df-3an 1081 df-tru 1531 df-ex 1772 df-nf 1776 df-sb 2061 df-mo 2615 df-eu 2647 df-clab 2797 df-cleq 2811 df-clel 2890 df-nfc 2960 df-ne 3014 df-ral 3140 df-rex 3141 df-reu 3142 df-rab 3144 df-v 3494 df-sbc 3770 df-dif 3936 df-un 3938 df-in 3940 df-ss 3949 df-pss 3951 df-nul 4289 df-if 4464 df-pw 4537 df-sn 4558 df-pr 4560 df-tp 4562 df-op 4564 df-uni 4831 df-int 4868 df-br 5058 df-opab 5120 df-mpt 5138 df-tr 5164 df-id 5453 df-eprel 5458 df-po 5467 df-so 5468 df-fr 5507 df-we 5509 df-xp 5554 df-rel 5555 df-cnv 5556 df-co 5557 df-dm 5558 df-rn 5559 df-res 5560 df-ima 5561 df-ord 6187 df-on 6188 df-lim 6189 df-suc 6190 df-iota 6307 df-fun 6350 df-fn 6351 df-f 6352 df-f1 6353 df-fo 6354 df-f1o 6355 df-fv 6356 df-om 7570 df-1o 8091 df-er 8278 df-en 8498 df-dom 8499 df-sdom 8500 df-fin 8501 df-card 9356 |
This theorem is referenced by: cardsn 9386 |
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