lean-ja / lean-ja/lean-by-example
unseal コマンド使用例：decidable なのに decide で示せない例
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宣言的コマンド
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Description
import Mathlib
example : Nat.log2 4 = 2 := by
-- decide で示すことができない
fail_if_success decide
simp [Nat.log2]
-- これは通るので Decidable のインスタンスではある
-- なぜ上記の命題を decide で示せないのかというと、
-- reducible ではないから。
#eval decide (Nat.log2 4 = 2)
-- unseal すると decide で示せるようになる
unseal Nat.log2 in
example : Nat.log2 4 = 2 := by
decide
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.
- Open a pull request that references the issue number.
Research direction
No file or test is named. Start by locating where this repository keeps Lean examples, then review the unseal, decide, and Nat.log2 snippet from the issue. Done means the example clearly shows why decide fails before unsealing and succeeds afterward.
Written by the indexing model from the issue text.
Assessment
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- documentation
- Issue type
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- Newbie friendliness
- 35/100