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[Merged by Bors] - feat(GroupTheory/SpecificGroups/AlternatingGroup): subgroups of index 2 of Equiv.Perm#21190

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[Merged by Bors] - feat(GroupTheory/SpecificGroups/AlternatingGroup): subgroups of index 2 of Equiv.Perm#21190
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@AntoineChambert-Loir AntoineChambert-Loir commented Jan 28, 2025

A subgroup of index 2 of Equiv.Perm αis equal to alternatingGroup α,
a subgroup of index at most 2 contains it.


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@github-actions github-actions bot added the large-import Automatically added label for PRs with a significant increase in transitive imports label Jan 28, 2025
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github-actions bot commented Jan 28, 2025

PR summary 9880f01586

Import changes for modified files

Dependency changes

File Base Count Head Count Change
Mathlib.GroupTheory.SpecificGroups.Alternating 948 951 +3 (+0.32%)
Import changes for all files
Files Import difference
Mathlib.GroupTheory.SpecificGroups.Alternating 3

Declarations diff

+ alternatingGroup.index_eq_two
+ alternatingGroup_le_of_index_le_two
+ eq_alternatingGroup_of_index_eq_two
+ eq_bot_of_card_le_two
+ index_eq_one
+ instance : (alternatingGroup α).Characteristic

You can run this locally as follows
## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.


No changes to technical debt.

You can run this locally as

./scripts/technical-debt-metrics.sh pr_summary
  • The relative value is the weighted sum of the differences with weight given by the inverse of the current value of the statistic.
  • The absolute value is the relative value divided by the total sum of the inverses of the current values (i.e. the weighted average of the differences).

@github-actions github-actions bot added the t-algebra Algebra (groups, rings, fields, etc) label Jan 28, 2025
@AntoineChambert-Loir AntoineChambert-Loir changed the title feat(GroupTheory/SpecificGroups/AlternatingGroup): subgroup of index at most 2 feat(GroupTheory/SpecificGroups/AlternatingGroup): subgroups of index 2 of Equiv.Perm Jan 28, 2025
@mathlib4-dependent-issues-bot mathlib4-dependent-issues-bot added the blocked-by-other-PR This PR depends on another PR (this label is automatically managed by a bot) label Jan 28, 2025
Delete the property that the alternating subgroup is characteristic. I'll prove it later from the results here. (Either in this PR or in a subsequent one).
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alreadydone commented Jan 29, 2025

I've been able to golf is_alternatingGroup_of_index_eq_two and use it to prove alternatingGroup.isCharacteristic in this commit.

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(note that Mathlib.GroupTheory.SpecificGroups.Alternating is a leaf file, so the large import label is not an issue)

@AntoineChambert-Loir AntoineChambert-Loir removed the blocked-by-other-PR This PR depends on another PR (this label is automatically managed by a bot) label Jan 31, 2025
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@leanprover-community-bot-assistant leanprover-community-bot-assistant added the merge-conflict The PR has a merge conflict with master, and needs manual merging. (this label is managed by a bot) label Jan 31, 2025
@leanprover-community-bot-assistant leanprover-community-bot-assistant removed the merge-conflict The PR has a merge conflict with master, and needs manual merging. (this label is managed by a bot) label Jan 31, 2025
@github-actions github-actions bot removed the large-import Automatically added label for PRs with a significant increase in transitive imports label Jan 31, 2025
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Thanks 🎉
maintainer delegate

simp_rw [mem_top, Nat.card_eq_fintype_card]; rfl

@[nontriviality]
theorem index_eq_one [Subsingleton α] : (alternatingGroup α).index = 1 := by
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Suggested change
theorem index_eq_one [Subsingleton α] : (alternatingGroup α).index = 1 := by
theorem alternatingGroup.index_eq_one [Subsingleton α] : (alternatingGroup α).index = 1 := by


open Subgroup Group

/-- The alternating group is the only subgroup of index 2 of the permutation group -/
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I'd add a period after these full sentences in docstrings. (2 more below)

Suggested change
/-- The alternating group is the only subgroup of index 2 of the permutation group -/
/-- The alternating group is the only subgroup of index 2 of the permutation group. -/

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🚀 Pull request has been placed on the maintainer queue by alreadydone.

@github-actions github-actions bot added the maintainer-merge A reviewer has approved the changed; awaiting maintainer approval. label Jan 31, 2025
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Thanks!

bors d+

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mathlib-bors bot commented Jan 31, 2025

✌️ AntoineChambert-Loir can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

@ghost ghost added delegated This pull request has been delegated to the PR author (or occasionally another non-maintainer). and removed maintainer-merge A reviewer has approved the changed; awaiting maintainer approval. labels Jan 31, 2025
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AntoineChambert-Loir commented Jan 31, 2025 via email

mathlib-bors bot pushed a commit that referenced this pull request Jan 31, 2025
… 2 of Equiv.Perm (#21190)

A subgroup of index  2 of `Equiv.Perm  α`is equal to `alternatingGroup α`,
a subgroup of index at most 2 contains it.
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mathlib-bors bot commented Jan 31, 2025

Pull request successfully merged into master.

Build succeeded:

@mathlib-bors mathlib-bors bot changed the title feat(GroupTheory/SpecificGroups/AlternatingGroup): subgroups of index 2 of Equiv.Perm [Merged by Bors] - feat(GroupTheory/SpecificGroups/AlternatingGroup): subgroups of index 2 of Equiv.Perm Jan 31, 2025
@mathlib-bors mathlib-bors bot closed this Jan 31, 2025
@mathlib-bors mathlib-bors bot deleted the ACL-J/alternatingIndex branch January 31, 2025 14:18
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tb65536 commented Feb 1, 2025

@AntoineChambert-Loir You seem to have merged this PR without responding to @alreadydone's comments. Can you open a new PR with those changes?

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AntoineChambert-Loir commented Feb 1, 2025

@tb65536 I am sorry. #21314

Julian added a commit that referenced this pull request Feb 2, 2025
* factorial-dvd-int: (143 commits)
  Apply suggestions from code review
  feat(Factorial): k! divides the product of any k successive integers
  feat(CategoryTheory): creation of finite limits (#21320)
  chore: update Mathlib dependencies 2025-02-01 (#21328)
  chore(GroupTheory/SpecificGroups/Alternating.lean): follow last minute review of JX (#21314)
  feat: `‖x‖ₑ.toNNReal = ‖x‖₊` (#21306)
  chore: cleanup imports in Archive/IfNormalization (#21318)
  doc: fix several typos (#21315)
  feat(CategoryTheory): transfer being iso along an iso in the arrow category (#21310)
  chore: delete declarations deprecated between 2024-01 and 2024-07 (#21271)
  feat(Analysis/Normed/Module/Dual): polar in a normed space as a submodule (#20084)
  chore(Data/ZMod/Basic): split `ZMod.valMinAbs` off (#21308)
  feat(GroupTheory/Perm/Centralizer): study the centralizer of a permutation (#17522)
  feat(RingTheory/LocalRing): `IsLocalRing` for subrings (#21168)
  chore: update Mathlib dependencies 2025-02-01 (#21312)
  chore: update Mathlib dependencies 2025-01-31 (#21311)
  feat: generalize `mem_dite` to `Membership α β` (#21262)
  feat: Lemmas for some monomial orders (#16177)
  feat(CategoryTheory): the localized category is monoidal (#12728)
  feat: add function log⁺ (=positive part of the logarithm) and prove standard estimates (#21289)
  feat(RingTheory/WittVector): ring of Witt vectors is p-adically complete (#21295)
  feat(GroupTheory/GroupAction/Blocks): more on blocks (#21284)
  fix(FieldTheory/KrullTopology): make `krullTopology_discreteTopology_of_finiteDimensional` universe polymorphic (#21299)
  feat(RingTheory/Artinian): integral non-zero-divisors are units over artinian rings (#21199)
  refactor(Topology/Gluing): simplify definition of `TopCat.GlueData.Rel` (#20653)
  feat(RingTheory/PowerSeries): binomial series (#20192)
  chore(Mathlib/RingTheory/MvPolynomial): rename MonomiaOrder.lCoeff to MonomialOrder.leadingCoeff  (#21290)
  chore (RingTheory/HahnSeries): fix names that use coeff (#21279)
  feat: let `notation3` distinguish `Prop` vs `Type _ ` vs `Sort _` (#21233)
  chore(MeasureTheory/Function/StronglyMeasurable): split Basic into Basic and AEStronglyMeasurable (#21273)
  feat(CategoryTheory): the monoidal category structure on a localization (#20951)
  feat(Analysis/Complex/Hadamard): generalize Hadamard's three lines theorem (#15009)
  feat(Order/CompleteBooleanAlgebra): Himp in terms of sSup (#20328)
  feat(ENNReal/Basic): add `ofNat_ne_top` and `top_ne_ofNat` (#14486)
  feat: Function.const as a PartialEquiv (#21137)
  chore(NonZeroDivisors): don't import rings (#20871)
  feat(Data/Set/Lattice): insert distributivity with iUnion/iInter (#21267)
  feat(GroupTheory/SpecificGroups/AlternatingGroup): subgroups of index 2 of Equiv.Perm (#21190)
  feat(GroupTheory/GroupAction/Transitive): basic results on transitive actions (#21285)
  perf(MeasureTheory/Function/LpSpace.lean): speed up (#21179)
  feat(Order): order isomorphisms from `Fin n` for small `n` (#21120)
  refactor(Topology/Group): turn morphisms in ProfiniteGrp into one field structures (#20740)
  feat: Sylow's first theorem for elementary `p`-groups (#21072)
  chore(Submonoid/Membership): don't import `MonoidWithZero` (#20748)
  refactor(Algebra/Algebra/Pi): cleanup and renaming (#21213)
  feat(GroupTheory/IndexNormal): subgroups of small index are normal (#21186)
  feat(Algebra/Group/Action): add definition of equidecomposition (#16936)
  feat(CategoryTheory/Subpresheaf): equalizer (#21096)
  feat: add lemmas about products of `Matrix.stdBasisMatrix` (#21204)
  chore: update Mathlib dependencies 2025-01-31 (#21282)
  ...
jt496 pushed a commit that referenced this pull request Feb 3, 2025
… 2 of Equiv.Perm (#21190)

A subgroup of index  2 of `Equiv.Perm  α`is equal to `alternatingGroup α`,
a subgroup of index at most 2 contains it.
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