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Mirrors > Home > ILE Home > Th. List > Mathboxes > bj-notbi | GIF version |
Description: Equivalence property for negation. TODO: minimize all theorems using notbid 592 and notbii 594. (Contributed by BJ, 27-Jan-2020.) (Proof modification is discouraged.) |
Ref | Expression |
---|---|
bj-notbi | ⊢ ((𝜑 ↔ 𝜓) → (¬ 𝜑 ↔ ¬ 𝜓)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | bi2 121 | . . 3 ⊢ ((𝜑 ↔ 𝜓) → (𝜓 → 𝜑)) | |
2 | 1 | con3d 561 | . 2 ⊢ ((𝜑 ↔ 𝜓) → (¬ 𝜑 → ¬ 𝜓)) |
3 | bi1 111 | . . 3 ⊢ ((𝜑 ↔ 𝜓) → (𝜑 → 𝜓)) | |
4 | 3 | con3d 561 | . 2 ⊢ ((𝜑 ↔ 𝜓) → (¬ 𝜓 → ¬ 𝜑)) |
5 | 2, 4 | impbid 120 | 1 ⊢ ((𝜑 ↔ 𝜓) → (¬ 𝜑 ↔ ¬ 𝜓)) |
Colors of variables: wff set class |
Syntax hints: ¬ wn 3 → wi 4 ↔ wb 98 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 99 ax-ia2 100 ax-ia3 101 ax-in1 544 ax-in2 545 |
This theorem depends on definitions: df-bi 110 |
This theorem is referenced by: bj-notbii 10046 bj-notbid 10047 bj-dcbi 10048 |
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