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| Mirrors > Home > MPE Home > Th. List > biid | Structured version Visualization version GIF version | ||
| Description: Principle of identity for logical equivalence. Theorem *4.2 of [WhiteheadRussell] p. 117. This is part of Frege's eighth axiom per Proposition 54 of [Frege1879] p. 50; see also eqid 2737. (Contributed by NM, 2-Jun-1993.) |
| Ref | Expression |
|---|---|
| biid | ⊢ (𝜑 ↔ 𝜑) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | id 22 | . 2 ⊢ (𝜑 → 𝜑) | |
| 2 | 1, 1 | impbii 209 | 1 ⊢ (𝜑 ↔ 𝜑) |
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