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Mirrors > Home > MPE Home > Th. List > exists1 | Structured version Visualization version GIF version |
Description: Two ways to express "only one thing exists." The left-hand side requires only one variable to express this. Both sides are false in set theory; see theorem dtru 4857. (Contributed by NM, 5-Apr-2004.) |
Ref | Expression |
---|---|
exists1 | ⊢ (∃!𝑥 𝑥 = 𝑥 ↔ ∀𝑥 𝑥 = 𝑦) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-eu 2474 | . 2 ⊢ (∃!𝑥 𝑥 = 𝑥 ↔ ∃𝑦∀𝑥(𝑥 = 𝑥 ↔ 𝑥 = 𝑦)) | |
2 | equid 1939 | . . . . . 6 ⊢ 𝑥 = 𝑥 | |
3 | 2 | tbt 359 | . . . . 5 ⊢ (𝑥 = 𝑦 ↔ (𝑥 = 𝑦 ↔ 𝑥 = 𝑥)) |
4 | bicom 212 | . . . . 5 ⊢ ((𝑥 = 𝑦 ↔ 𝑥 = 𝑥) ↔ (𝑥 = 𝑥 ↔ 𝑥 = 𝑦)) | |
5 | 3, 4 | bitri 264 | . . . 4 ⊢ (𝑥 = 𝑦 ↔ (𝑥 = 𝑥 ↔ 𝑥 = 𝑦)) |
6 | 5 | albii 1747 | . . 3 ⊢ (∀𝑥 𝑥 = 𝑦 ↔ ∀𝑥(𝑥 = 𝑥 ↔ 𝑥 = 𝑦)) |
7 | 6 | exbii 1774 | . 2 ⊢ (∃𝑦∀𝑥 𝑥 = 𝑦 ↔ ∃𝑦∀𝑥(𝑥 = 𝑥 ↔ 𝑥 = 𝑦)) |
8 | nfae 2316 | . . 3 ⊢ Ⅎ𝑦∀𝑥 𝑥 = 𝑦 | |
9 | 8 | 19.9 2072 | . 2 ⊢ (∃𝑦∀𝑥 𝑥 = 𝑦 ↔ ∀𝑥 𝑥 = 𝑦) |
10 | 1, 7, 9 | 3bitr2i 288 | 1 ⊢ (∃!𝑥 𝑥 = 𝑥 ↔ ∀𝑥 𝑥 = 𝑦) |
Colors of variables: wff setvar class |
Syntax hints: ↔ wb 196 ∀wal 1481 ∃wex 1704 ∃!weu 2470 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1722 ax-4 1737 ax-5 1839 ax-6 1888 ax-7 1935 ax-10 2019 ax-11 2034 ax-12 2047 ax-13 2246 |
This theorem depends on definitions: df-bi 197 df-or 385 df-an 386 df-tru 1486 df-ex 1705 df-nf 1710 df-eu 2474 |
This theorem is referenced by: exists2 2562 |
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