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Mirrors > Home > ILE Home > Th. List > ax-9 | GIF version |
Description: Derive ax-9 1512 from ax-i9 1511, the modified version for intuitionistic logic. Although ax-9 1512 does hold intuistionistically, in intuitionistic logic it is weaker than ax-i9 1511. (Contributed by NM, 3-Feb-2015.) |
Ref | Expression |
---|---|
ax-9 | ⊢ ¬ ∀𝑥 ¬ 𝑥 = 𝑦 |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ax-i9 1511 | . . 3 ⊢ ∃𝑥 𝑥 = 𝑦 | |
2 | 1 | notnoti 635 | . 2 ⊢ ¬ ¬ ∃𝑥 𝑥 = 𝑦 |
3 | alnex 1476 | . 2 ⊢ (∀𝑥 ¬ 𝑥 = 𝑦 ↔ ¬ ∃𝑥 𝑥 = 𝑦) | |
4 | 2, 3 | mtbir 661 | 1 ⊢ ¬ ∀𝑥 ¬ 𝑥 = 𝑦 |
Colors of variables: wff set class |
Syntax hints: ¬ wn 3 ∀wal 1330 = wceq 1332 ∃wex 1469 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-ia1 105 ax-ia2 106 ax-ia3 107 ax-in1 604 ax-in2 605 ax-5 1424 ax-gen 1426 ax-ie2 1471 ax-i9 1511 |
This theorem depends on definitions: df-bi 116 df-tru 1335 df-fal 1338 |
This theorem is referenced by: equidqe 1513 |
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