| Metamath Proof Explorer |
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Related theorems GIF version |
| Description: A mixed syllogism inference from a nested implication and a biconditional. Useful for substituting an embedded antecedent with a definition. |
| Ref | Expression |
|---|---|
| syl5ib.1 | ⊢ (φ → (ψ → χ)) |
| syl5ib.2 | ⊢ (θ ↔ ψ) |
| Ref | Expression |
|---|---|
| syl5ib | ⊢ (φ → (θ → χ)) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | syl5ib.1 | . 2 ⊢ (φ → (ψ → χ)) | |
| 2 | syl5ib.2 | . . 3 ⊢ (θ ↔ ψ) | |
| 3 | 2 | biimpi 149 | . 2 ⊢ (θ → ψ) |
| 4 | 1, 3 | syl5 21 | 1 ⊢ (φ → (θ → χ)) |