leanprover / leanprover/lean4

`revert` does not respect the argument order

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#3,028 2 comments 2 reactions 0 assignees View on GitHub

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Description

Prerequisites
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Description

The revert tactic ignores the order of its arguments

Context

[Broader context that the issue occured in. If there was any prior discussion on the Lean Zulip, link it here as well.]

Steps to Reproduce
example (a b c : Nat) : a * b * c = 1 := by
  revert c a b
  sorry

Expected behavior: Goal is ∀ (c a b : Nat), a * b * c = 1 like it was in Lean 3

Actual behavior: Goal is ∀ (a b c : Nat), a * b * c = 1, ignoring the argument order

Versions

4.4.0-rc1

Impact

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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 minimal revert c a b example in the issue and compare the produced goal with the expected order. Locate the Lean 4 revert tactic implementation, then add a regression test showing that argument order is preserved and run the relevant tactic tests.

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
Clearly specified
Newbie friendliness
45/100

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