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| Mirrors > Home > MPE Home > Th. List > Mathboxes > xfree2 | Structured version Visualization version GIF version | ||
| Description: A partial converse to 19.9t 2203. (Contributed by Stefan Allan, 21-Dec-2008.) | 
| Ref | Expression | 
|---|---|
| xfree2 | ⊢ (∀𝑥(𝜑 → ∀𝑥𝜑) ↔ ∀𝑥(¬ 𝜑 → ∀𝑥 ¬ 𝜑)) | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | xfree 32464 | . 2 ⊢ (∀𝑥(𝜑 → ∀𝑥𝜑) ↔ ∀𝑥(∃𝑥𝜑 → 𝜑)) | |
| 2 | eximal 1781 | . . 3 ⊢ ((∃𝑥𝜑 → 𝜑) ↔ (¬ 𝜑 → ∀𝑥 ¬ 𝜑)) | |
| 3 | 2 | albii 1818 | . 2 ⊢ (∀𝑥(∃𝑥𝜑 → 𝜑) ↔ ∀𝑥(¬ 𝜑 → ∀𝑥 ¬ 𝜑)) | 
| 4 | 1, 3 | bitri 275 | 1 ⊢ (∀𝑥(𝜑 → ∀𝑥𝜑) ↔ ∀𝑥(¬ 𝜑 → ∀𝑥 ¬ 𝜑)) | 
| Colors of variables: wff setvar class | 
| Syntax hints: ¬ wn 3 → wi 4 ↔ wb 206 ∀wal 1537 ∃wex 1778 | 
| This theorem was proved from axioms: ax-mp 5 ax-1 6 ax-2 7 ax-3 8 ax-gen 1794 ax-4 1808 ax-5 1909 ax-6 1966 ax-7 2006 ax-10 2140 ax-12 2176 | 
| This theorem depends on definitions: df-bi 207 df-or 848 df-ex 1779 df-nf 1783 | 
| This theorem is referenced by: (None) | 
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