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| Mirrors > Home > ILE Home > Th. List > ecased | GIF version | ||
| Description: Deduction form of disjunctive syllogism. (Contributed by Jim Kingdon, 9-Dec-2017.) | 
| Ref | Expression | 
|---|---|
| ecased.1 | ⊢ (𝜑 → ¬ 𝜒) | 
| ecased.2 | ⊢ (𝜑 → (𝜓 ∨ 𝜒)) | 
| Ref | Expression | 
|---|---|
| ecased | ⊢ (𝜑 → 𝜓) | 
| Step | Hyp | Ref | Expression | 
|---|---|---|---|
| 1 | ecased.1 | . . 3 ⊢ (𝜑 → ¬ 𝜒) | |
| 2 | ecased.2 | . . 3 ⊢ (𝜑 → (𝜓 ∨ 𝜒)) | |
| 3 | 1, 2 | jca 306 | . 2 ⊢ (𝜑 → (¬ 𝜒 ∧ (𝜓 ∨ 𝜒))) | 
| 4 | orel2 727 | . . 3 ⊢ (¬ 𝜒 → ((𝜓 ∨ 𝜒) → 𝜓)) | |
| 5 | 4 | imp 124 | . 2 ⊢ ((¬ 𝜒 ∧ (𝜓 ∨ 𝜒)) → 𝜓) | 
| 6 | 3, 5 | syl 14 | 1 ⊢ (𝜑 → 𝜓) | 
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