leanprover / leanprover/lean4

Deep kernel reduction detected after `simp`

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bug P-medium
Dominant language
Lean
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Description

Prerequisites

Please put an X between the brackets as you perform the following steps:

Description

The following lean code leads to a deep kernel reduction detected error in Lean.

theorem minimal6 : ∀ (x : BitVec 32),
  ((some x).bind fun x =>
    (if False then none else some (x.sshiftRight 1)).bind fun x' =>
      some (x'.sshiftRight 1))
  = (some x) := by
  intro x
  simp only [Option.some_bind]
  sorry
Steps to Reproduce
  1. Copy into lean
  2. Observe the red line under the theorem name

Expected behavior: [Clear and concise description of what you expect to happen]

  • simp should apply the lemma
  • the proof should be marked as sorry with an orange line under the theorem name
  • no kernel error
Versions

"4.12.0-nightly-2024-10-15"

Impact

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This issue was reduced by @lfrenot.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the minimal6 theorem and reproduce it using Lean version 4.12.0-nightly-2024-10-15. Investigate the interaction between simp, Option.some_bind, BitVec.sshiftRight, and kernel reduction. Done means simp applies the lemma, the proof remains marked sorry, and no deep kernel reduction error is reported.

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
Mostly clear
Newbie friendliness
35/100

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