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Mirrors > Home > MPE Home > Th. List > id | Structured version Visualization version GIF version |
Description: Principle of identity. Theorem *2.08 of [WhiteheadRussell] p. 101. For another version of the proof directly from axioms, see idALT 23. Its associated inference, idi 1, requires no axioms for its proof, contrary to id 22. Note that the second occurrences of 𝜑 in Steps 1 and 2 may be simultaneously replaced by any wff 𝜓, which may ease the understanding of the proof. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Stefan Allan, 20-Mar-2006.) |
Ref | Expression |
---|---|
id | ⊢ (𝜑 → 𝜑) |
Step | Hyp | Ref | Expression |
---|---|---|---|
1 | ax-1 6 | . 2 ⊢ (𝜑 → (𝜑 → 𝜑)) | |
2 | ax-1 6 | . 2 ⊢ (𝜑 → ((𝜑 → 𝜑) → 𝜑)) | |
3 | 1, 2 | mpd 15 | 1 ⊢ (𝜑 → 𝜑) |
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