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Mirrors > Home > MPE Home > Th. List > Mathboxes > bj-dfnnf3 | Structured version Visualization version GIF version |
Description: Alternate definition of nonfreeness when sp 2181 is available. (Contributed by BJ, 28-Jul-2023.) The proof should not rely on df-nf 1781. (Proof modification is discouraged.) |
Ref | Expression |
---|---|
bj-dfnnf3 | ⊢ (Ⅎ'𝑥𝜑 ↔ (∃𝑥𝜑 → ∀𝑥𝜑)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | bj-nnfea 36717 | . 2 ⊢ (Ⅎ'𝑥𝜑 → (∃𝑥𝜑 → ∀𝑥𝜑)) | |
2 | bj-19.21bit 36673 | . . 3 ⊢ ((∃𝑥𝜑 → ∀𝑥𝜑) → (∃𝑥𝜑 → 𝜑)) | |
3 | bj-19.23bit 36674 | . . 3 ⊢ ((∃𝑥𝜑 → ∀𝑥𝜑) → (𝜑 → ∀𝑥𝜑)) | |
4 | df-bj-nnf 36707 | . . 3 ⊢ (Ⅎ'𝑥𝜑 ↔ ((∃𝑥𝜑 → 𝜑) ∧ (𝜑 → ∀𝑥𝜑))) | |
5 | 2, 3, 4 | sylanbrc 583 | . 2 ⊢ ((∃𝑥𝜑 → ∀𝑥𝜑) → Ⅎ'𝑥𝜑) |
6 | 1, 5 | impbii 209 | 1 ⊢ (Ⅎ'𝑥𝜑 ↔ (∃𝑥𝜑 → ∀𝑥𝜑)) |
Colors of variables: wff setvar class |
Syntax hints: → wi 4 ↔ wb 206 ∀wal 1535 ∃wex 1776 Ⅎ'wnnf 36706 |
This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1792 ax-4 1806 ax-5 1908 ax-6 1965 ax-7 2005 ax-12 2175 |
This theorem depends on definitions: df-bi 207 df-an 396 df-ex 1777 df-bj-nnf 36707 |
This theorem is referenced by: bj-nfnnfTEMP 36741 |
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