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Mirrors > Home > MPE Home > Th. List > eu6 | Structured version Visualization version GIF version |
Description: Alternate definition of the unique existential quantifier df-eu 2564 not using the at-most-one quantifier. (Contributed by NM, 12-Aug-1993.) This used to be the definition of the unique existential quantifier, while df-eu 2564 was then proved as dfeu 2590. (Revised by BJ, 30-Sep-2022.) (Proof shortened by Wolf Lammen, 3-Jan-2023.) Remove use of ax-11 2155. (Revised by SN, 21-Sep-2023.) |
Ref | Expression |
---|---|
eu6 | ⊢ (∃!𝑥𝜑 ↔ ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | dfmoeu 2531 | . . . 4 ⊢ ((∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) ↔ ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦)) | |
2 | 1 | anbi2i 624 | . . 3 ⊢ ((∃𝑥𝜑 ∧ (∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦))) ↔ (∃𝑥𝜑 ∧ ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦))) |
3 | abai 826 | . . 3 ⊢ ((∃𝑥𝜑 ∧ ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) ↔ (∃𝑥𝜑 ∧ (∃𝑥𝜑 → ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)))) | |
4 | eu3v 2565 | . . 3 ⊢ (∃!𝑥𝜑 ↔ (∃𝑥𝜑 ∧ ∃𝑦∀𝑥(𝜑 → 𝑥 = 𝑦))) | |
5 | 2, 3, 4 | 3bitr4ri 304 | . 2 ⊢ (∃!𝑥𝜑 ↔ (∃𝑥𝜑 ∧ ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦))) |
6 | abai 826 | . . 3 ⊢ ((∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) ∧ ∃𝑥𝜑) ↔ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) ∧ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) → ∃𝑥𝜑))) | |
7 | ancom 462 | . . 3 ⊢ ((∃𝑥𝜑 ∧ ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) ↔ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) ∧ ∃𝑥𝜑)) | |
8 | biimpr 219 | . . . . . . 7 ⊢ ((𝜑 ↔ 𝑥 = 𝑦) → (𝑥 = 𝑦 → 𝜑)) | |
9 | 8 | alimi 1814 | . . . . . 6 ⊢ (∀𝑥(𝜑 ↔ 𝑥 = 𝑦) → ∀𝑥(𝑥 = 𝑦 → 𝜑)) |
10 | 9 | eximi 1838 | . . . . 5 ⊢ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) → ∃𝑦∀𝑥(𝑥 = 𝑦 → 𝜑)) |
11 | exsbim 2006 | . . . . 5 ⊢ (∃𝑦∀𝑥(𝑥 = 𝑦 → 𝜑) → ∃𝑥𝜑) | |
12 | 10, 11 | syl 17 | . . . 4 ⊢ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) → ∃𝑥𝜑) |
13 | 12 | biantru 531 | . . 3 ⊢ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) ↔ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) ∧ (∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦) → ∃𝑥𝜑))) |
14 | 6, 7, 13 | 3bitr4i 303 | . 2 ⊢ ((∃𝑥𝜑 ∧ ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) ↔ ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) |
15 | 5, 14 | bitri 275 | 1 ⊢ (∃!𝑥𝜑 ↔ ∃𝑦∀𝑥(𝜑 ↔ 𝑥 = 𝑦)) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ↔ wb 205 ∧ wa 397 ∀wal 1540 ∃wex 1782 ∃!weu 2563 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1798 ax-4 1812 ax-5 1914 ax-6 1972 ax-7 2012 ax-10 2138 ax-12 2172 |
This theorem depends on definitions: df-bi 206 df-an 398 df-or 847 df-ex 1783 df-nf 1787 df-mo 2535 df-eu 2564 |
This theorem is referenced by: euf 2571 nfeu1 2583 dfmo 2591 sb8eulem 2593 reu6 3723 euabsn2 4730 eunex 5389 euotd 5514 iotauni 6519 iota1 6521 iotanul 6522 iotaexOLD 6524 iota4 6525 fv3 6910 eufnfv 7231 seqomlem2 8451 aceq1 10112 dfac5 10123 bnj89 33732 cbveud 36253 wl-eudf 36437 wl-euequf 36439 wl-sb8eut 36442 iotain 43176 iotaexeu 43177 iotasbc 43178 iotavalsb 43192 sbiota1 43193 eusnsn 45736 mo0sn 47500 |
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