lean-ja / lean-ja/lean-by-example
defeq と propeq の違いはなぜあるのか
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Description
たとえば x : T があるとする。
このとき x : C であるかどうか判定しようとしたとき、T = C を propeq の意味で証明するのは難しいが、defeq の意味で等しいか判定するのは計算量的に簡単。
したがって、defeq と propeq の区別がないと、型の検査が激重になってしまう。
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
Start by reviewing the repository's existing Lean examples and mdBook reference material for type checking, defeq, and propeq. The work is complete when the material clearly explains why the two notions are distinct and how that distinction affects checking whether x : C holds when x : T.
Written by the indexing model from the issue text.
Assessment
- Domain
- documentation
- Issue type
- Documentation
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Quiet
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100