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Mirrors > Home > ILE Home > Th. List > pm4.83dc | GIF version |
Description: Theorem *4.83 of [WhiteheadRussell] p. 122, for decidable propositions. As with other case elimination theorems, like pm2.61dc 762, it only holds for decidable propositions. (Contributed by Jim Kingdon, 12-May-2018.) |
Ref | Expression |
---|---|
pm4.83dc | ⊢ (DECID 𝜑 → (((𝜑 → 𝜓) ∧ (¬ 𝜑 → 𝜓)) ↔ 𝜓)) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | df-dc 743 | . . 3 ⊢ (DECID 𝜑 ↔ (𝜑 ∨ ¬ 𝜑)) | |
2 | pm3.44 635 | . . . 4 ⊢ (((𝜑 → 𝜓) ∧ (¬ 𝜑 → 𝜓)) → ((𝜑 ∨ ¬ 𝜑) → 𝜓)) | |
3 | 2 | com12 27 | . . 3 ⊢ ((𝜑 ∨ ¬ 𝜑) → (((𝜑 → 𝜓) ∧ (¬ 𝜑 → 𝜓)) → 𝜓)) |
4 | 1, 3 | sylbi 114 | . 2 ⊢ (DECID 𝜑 → (((𝜑 → 𝜓) ∧ (¬ 𝜑 → 𝜓)) → 𝜓)) |
5 | ax-1 5 | . . 3 ⊢ (𝜓 → (𝜑 → 𝜓)) | |
6 | ax-1 5 | . . 3 ⊢ (𝜓 → (¬ 𝜑 → 𝜓)) | |
7 | 5, 6 | jca 290 | . 2 ⊢ (𝜓 → ((𝜑 → 𝜓) ∧ (¬ 𝜑 → 𝜓))) |
8 | 4, 7 | impbid1 130 | 1 ⊢ (DECID 𝜑 → (((𝜑 → 𝜓) ∧ (¬ 𝜑 → 𝜓)) ↔ 𝜓)) |
Colors of variables: wff set class |
Syntax hints: ¬ wn 3 → wi 4 ∧ wa 97 ↔ wb 98 ∨ wo 629 DECID wdc 742 |
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-io 630 |
This theorem depends on definitions: df-bi 110 df-dc 743 |
This theorem is referenced by: (None) |
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