leanprover-community / leanprover-community/mathlib4
`zify` incorrectly uses `Eq.refl`
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Description
In Lean 3 we had:
import tactic.zify
example (h : 0 = 0) : true :=
begin
zify at h, -- `h` is `(0 : ℤ) = 0`, not `true`.
fail_if_success { assumption, },
trivial,
end
but in Lean 4 we now have:
import Mathlib.Tactic.Zify
example (h : 0 = 0) : True := by
zify at h -- `h` has become `True`
assumption
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
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- 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 two examples using the Mathlib.Tactic.Zify import and inspect the zify tactic entry point. Compare the resulting type of h in Lean 4 with the Lean 3 behavior shown in the issue; done means an equality such as (0 : ℤ) = 0 is not changed into True by zify at h.
Written by the indexing model from the issue text.
Assessment
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100