internal exception #3 shown as follow-up error message
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bug
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- Dominant language
- Lean
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Description
Prerequisites
- Check that your issue is not already filed:
https://github.com/leanprover/lean4/issues - Reduce the issue to a minimal, self-contained, reproducible test case.
Avoid dependencies to Mathlib or Batteries. - Test your test case against the latest nightly release, for example on
https://live.lean-lang.org/#project=lean-nightly
(You can also use the settings there to switch to “Lean nightly”)
Description
universe u
class Primary {base: Type u}
variable [Primary]
theorem order_determined {base: Type u} [Primary (base := base)] :
true := sorry
internal exception #3
Versions
4.30.0-nightly-2026-03-05
Impact
My work on verifying my proof of Navier-Stokes global regularity is stalled, because it is to confusing to work with this error,
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 running the minimal self-contained Lean example from the issue against the reported nightly version and confirm the internal exception #3 output. Trace the diagnostic path for this reproducer; done means the example reports a useful user-facing error instead of the internal exception.
Written by the indexing model from the issue text.
Assessment
- Domain
- compilers
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100