leanprover-community / leanprover-community/mathlib4
Int.cast_negSucc makes norm_cast introduce Int.negSucc
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Description
import Mathlib.Data.Int.Cast.Defs
variable {R : Type _} [AddGroupWithOne R]
namespace Int
@[norm_cast] -- Removing this attribute fixes the issue
theorem cast_negSucc (n : ℕ) : (-[n+1] : R) = -(n + 1 : ℕ) :=
AddGroupWithOne.intCast_negSucc n
end Int
example (k : ℤ) : (-1 : R) = k := by
show_term norm_cast
-- ⊢ ((Int.negSucc 0) : R) = (k : R)
-- should be
-- ⊢ ((-1 : ℤ) : R) = (k : R)
sorry
Contributor guide
First steps
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- Open a pull request that references the issue number.
Research direction
Start with the provided Lean reproducer and inspect how the [norm_cast] attribute on Int.cast_negSucc affects the norm_cast output. The fix is complete when the example no longer introduces Int.negSucc and instead produces the expected cast of (-1 : ℤ).
Written by the indexing model from the issue text.
Assessment
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100