leanprover-community / leanprover-community/mathlib4
show tactic fails to reorder goals
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Description
This doesn't work
example (P Q : Prop) : P ∧ Q := by
constructor
show Q -- fails
sorry
sorry
but did in Lean 3:
example (P Q : Prop) : P ∧ Q :=
begin
constructor,
show Q, -- ok
sorry,
sorry,
end
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 Lean 4 example in the issue and compare it with the Lean 3 version. Investigate how constructor and show Q handle goal ordering, then verify that the Lean 4 example accepts show Q as shown and retains the two remaining goals.
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
- 35/100