Inconsistent substitution behavior of `cases`
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enhancement
low priority
P-low
- Dominant language
- Lean
- Stars
- 9.2k
- Forks
- 990
- Avg merge
- 1d 17h
- Merged PRs (30d)
- 175
Description
As noticed by @larsk21
example (h : n = 0) : n = 0 := by cases n -- replaces all occurrences
example (h : n = 0) : n = 0 := by cases h' : n -- replaces occurrence in target
example (h : id n = 0) : id n = 0 := by cases id n -- replaces occurrence in target
example (h : id n = 0) : id n = 0 := by cases h' : id n -- replaces occurrence in target
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 reproducing the four Lean examples from the issue and compare how cases n, cases h' : n, cases id n, and cases h' : id n substitute occurrences. Trace the relevant cases tactic behavior; done means the substitution rules are consistent or the intended distinction is clearly documented and tested.
Written by the indexing model from the issue text.
Assessment
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 35/100