lean-ja / lean-ja/lean-by-example
二重否定の除去の二重否定
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Description
タグ：命題論理、二重否定、直観主義、証明例
/-- 二重否定の除去の二重否定 -/
example (P : Prop) : ¬¬ (¬¬ P → P) := by
intro h
have : ¬ P := by
intro hp
suffices ¬¬P → P from by
contradiction
intro _
assumption
apply h
intro hn2p
contradiction
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
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Research direction
The issue provides only a Lean proof example and does not name a target file, test, or requested change. Start by locating where related proposition-logic examples are stored; the issue needs a defined placement and acceptance criterion before a newcomer can tell when the work is done.
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Assessment
- Domain
- documentation
- Issue type
- Documentation
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 20/100