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Mirrors > Home > ILE Home > Th. List > notnotbdc | GIF version |
Description: Double negation equivalence for a decidable proposition. Like Theorem *4.13 of [WhiteheadRussell] p. 117, but with a decidability antecendent. The forward direction, notnot 591, holds for all propositions, not just decidable ones. (Contributed by Jim Kingdon, 13-Mar-2018.) |
Ref | Expression |
---|---|
notnotbdc | ⊢ (DECID 𝜑 → (𝜑 ↔ ¬ ¬ 𝜑)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | notnot 591 | . 2 ⊢ (𝜑 → ¬ ¬ 𝜑) | |
2 | notnotrdc 784 | . 2 ⊢ (DECID 𝜑 → (¬ ¬ 𝜑 → 𝜑)) | |
3 | 1, 2 | impbid2 141 | 1 ⊢ (DECID 𝜑 → (𝜑 ↔ ¬ ¬ 𝜑)) |
Colors of variables: wff set class |
Syntax hints: ¬ wn 3 → wi 4 ↔ wb 103 DECID wdc 775 |
This theorem was proved from axioms: ax-1 5 ax-2 6 ax-mp 7 ax-ia1 104 ax-ia2 105 ax-ia3 106 ax-in1 576 ax-in2 577 ax-io 662 |
This theorem depends on definitions: df-bi 115 df-dc 776 |
This theorem is referenced by: con1biidc 804 imandc 819 imordc 829 dfbi3dc 1328 alexdc 1550 |
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