| Metamath Proof Explorer |
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Related theorems GIF version |
| Description: An inference from transitive law for logical equivalence. |
| Ref | Expression |
|---|---|
| bitr.1 | ⊢ (φ ↔ ψ) |
| bitr.2 | ⊢ (ψ ↔ χ) |
| Ref | Expression |
|---|---|
| bitr | ⊢ (φ ↔ χ) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | bitr.1 | . . . 4 ⊢ (φ ↔ ψ) | |
| 2 | 1 | biimp 151 | . . 3 ⊢ (φ → ψ) |
| 3 | bitr.2 | . . . 4 ⊢ (ψ ↔ χ) | |
| 4 | 3 | biimp 151 | . . 3 ⊢ (ψ → χ) |
| 5 | 2, 4 | syl 10 | . 2 ⊢ (φ → χ) |
| 6 | 3 | biimpr 152 | . . 3 ⊢ (χ → ψ) |
| 7 | 1 | biimpr 152 | . . 3 ⊢ (ψ → φ) |
| 8 | 6, 7 | syl 10 | . 2 ⊢ (χ → φ) |
| 9 | 5, 8 | impbi 157 | 1 ⊢ (φ ↔ χ) |