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Fix MinimalGeneratingSet for pc groups which sometimes returned incorrect (non-minimal) results#6340

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fingolfin merged 1 commit intomasterfrom
codex/issue-5771-minimalgeneratingset
May 4, 2026
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Fix MinimalGeneratingSet for pc groups which sometimes returned incorrect (non-minimal) results#6340
fingolfin merged 1 commit intomasterfrom
codex/issue-5771-minimalgeneratingset

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It sometimes produced incorrect results, where at least one generator was simply redundant.

Revisit the pc-group candidates when a layer contracts. This drops generators that were only needed earlier. Later layer adjustments can change the induced pcgs.

AI-assisted by Codex for investigation, testing, and implementation.

Fixes #5771.

It sometimes produced incorrect results, where at least one
generator was simply redundant.

Revisit the pc-group candidates when a layer contracts.
This drops generators that were only needed earlier.
Later layer adjustments can change the induced pcgs.

AI-assisted by Codex for investigation, testing, and implementation.

Co-authored-by: Codex <codex@openai.com>
@fingolfin fingolfin requested a review from hulpke April 21, 2026 23:20
@fingolfin fingolfin added kind: bug Issues describing general bugs, and PRs fixing them kind: bug: wrong result Issues describing bugs that result in mathematically or otherwise wrong results, and PRs fixing them topic: library release notes: use title For PRs: the title of this PR is suitable for direct use in the release notes labels Apr 21, 2026
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@hulpke @ThomasBreuer @ChrisJefferson @james-d-mitchell any thoughts on this?

@fingolfin fingolfin added this to the GAP 4.16.0 milestone Apr 29, 2026
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This certainly resolves one problem.

@fingolfin fingolfin merged commit 23c4dc7 into master May 4, 2026
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@fingolfin fingolfin deleted the codex/issue-5771-minimalgeneratingset branch May 4, 2026 18:28
cdwensley pushed a commit that referenced this pull request May 7, 2026
It sometimes produced incorrect results, where at least one
generator was simply redundant.

Revisit the pc-group candidates when a layer contracts.
This drops generators that were only needed earlier.
Later layer adjustments can change the induced pcgs.

AI-assisted by Codex for investigation, testing, and implementation.

Co-authored-by: Codex <codex@openai.com>
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kind: bug: wrong result Issues describing bugs that result in mathematically or otherwise wrong results, and PRs fixing them kind: bug Issues describing general bugs, and PRs fixing them release notes: use title For PRs: the title of this PR is suitable for direct use in the release notes topic: library

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Bug in MinimalGeneratingSet

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