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Mirrors > Home > MPE Home > Th. List > bitri | Structured version Visualization version GIF version |
Description: An inference from transitive law for logical equivalence. (Contributed by NM, 3-Jan-1993.) (Proof shortened by Wolf Lammen, 13-Oct-2012.) |
Ref | Expression |
---|---|
bitri.1 | ⊢ (𝜑 ↔ 𝜓) |
bitri.2 | ⊢ (𝜓 ↔ 𝜒) |
Ref | Expression |
---|---|
bitri | ⊢ (𝜑 ↔ 𝜒) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | bitri.1 | . . 3 ⊢ (𝜑 ↔ 𝜓) | |
2 | bitri.2 | . . 3 ⊢ (𝜓 ↔ 𝜒) | |
3 | 1, 2 | sylbb 218 | . 2 ⊢ (𝜑 → 𝜒) |
4 | 1, 2 | sylbbr 235 | . 2 ⊢ (𝜒 → 𝜑) |
5 | 3, 4 | impbii 208 | 1 ⊢ (𝜑 ↔ 𝜒) |
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