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| Mirrors > Home > MPE Home > Th. List > pm2.21 | Structured version Visualization version GIF version | ||
| Description: From a wff and its negation, anything follows. Theorem *2.21 of [WhiteheadRussell] p. 104. Also called the Duns Scotus law. Its commuted form is pm2.24 124 and its associated inference is pm2.21i 119. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Wolf Lammen, 14-Sep-2012.) |
| Ref | Expression |
|---|---|
| pm2.21 | ⊢ (¬ 𝜑 → (𝜑 → 𝜓)) |
| Step | Hyp | Ref | Expression |
|---|---|---|---|
| 1 | id 22 | . 2 ⊢ (¬ 𝜑 → ¬ 𝜑) | |
| 2 | 1 | pm2.21d 121 | 1 ⊢ (¬ 𝜑 → (𝜑 → 𝜓)) |
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