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feat(Algebra): maximal Cohen Macaulay module#29533

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feat(Algebra): maximal Cohen Macaulay module#29533
Thmoas-Guan wants to merge 2349 commits into
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Thmoas-Guan:maximal-CM-module

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@Thmoas-Guan Thmoas-Guan commented Sep 11, 2025

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In this PR, we defined the concept of maximal Cohen Macaulay module, and proved that finitely generated maximal Cohen Macaulay module over regular local ring is free.


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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 Sep 11, 2025
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PR summary b4d49cfc19

Import changes for modified files

No significant changes to the import graph

Import changes for all files
Files Import difference
Mathlib.RingTheory.RegularLocalRing.Basic (new file) 2193
Mathlib.RingTheory.Depth.Rees (new file) 2298
Mathlib.RingTheory.Depth.Basic (new file) 2300
Mathlib.RingTheory.Depth.Ischebeck (new file) 2338
Mathlib.RingTheory.CohenMacaulay.Basic (new file) 2443
Mathlib.RingTheory.CohenMacaulay.Maximal (new file) 2457

Declarations diff (regex)

+ FiniteRingKrullDim.ringKrullDim_eq_nat
+ Ideal.depth
+ Ideal.depth_eq_of_iso
+ Ideal.depth_eq_of_linearEquiv
+ Ideal.depth_eq_top_of_subsingleton
+ Ideal.depth_quotSMulTop_succ_eq_moduleDepth
+ Ideal.span_singleton_mul_eq_self_of_isPrime
+ IsCohenMacaulayLocalRing
+ IsCohenMacaulayLocalRing.of_isLocalRing_of_isCohenMacaulayRing
+ IsCohenMacaulayRing
+ IsCohenMacaulayRing.of_isCohenMacaulayLocalRing
+ IsDiscreteValuationRing.of_isRegularLocalRing_of_ringKrullDim_eq_one
+ IsLocalRing.depth
+ IsLocalRing.depth_eq_of_algebraMap_surjective
+ IsLocalRing.depth_eq_of_iso
+ IsLocalRing.depth_eq_of_linearEquiv
+ IsLocalRing.depth_eq_of_ringEquiv
+ IsLocalRing.depth_eq_sSup_length_regular
+ IsLocalRing.depth_eq_top_of_subsingleton
+ IsLocalRing.depth_quotSMulTop_succ_eq_moduleDepth
+ IsLocalRing.depth_quotient_regular_sequence_add_length_eq_depth
+ IsLocalRing.depth_quotient_regular_succ_eq_depth
+ IsLocalRing.depth_quotient_span_regular_succ_eq_depth
+ IsLocalRing.ideal_depth_eq_sSup_length_regular
+ IsLocalRing.ideal_depth_le_depth
+ IsLocalRing.spanFinrank_maximalIdeal_add_finrank_eq_of_surjective
+ IsLocalRing.spanFinrank_maximalIdeal_quotient
+ LinearMapOfSemiLinearMapAlgebraMap
+ ModuleCat.IsCohenMacaulay
+ ModuleCat.IsCohenMacaulay_of_iso
+ ModuleCat.IsMaximalCohenMacaulay
+ ModuleCat.depth_eq_supportDim_of_cohenMacaulay
+ ModuleCat.depth_eq_supportDim_unbot_of_cohenMacaulay
+ ModuleCat.isCohenMacaulay_iff
+ SemiLinearMapAlgebraMapOfLinearMap
+ Submodule.comap_lt_top_of_lt_range
+ associatedPrimes_self_eq_minimalPrimes
+ associated_prime_eq_minimalPrimes_isCohenMacaulay
+ associated_prime_minimal_of_isCohenMacaulay
+ depth_eq_dim_quotient_associated_prime_of_isCohenMacaulay
+ depth_le_ringKrullDim
+ depth_le_ringKrullDim_associatedPrime
+ depth_le_supportDim
+ depth_ne_top
+ depth_quotient_regular_sequence_add_length_eq_depth
+ exists_isRegular_of_exists_subsingleton_ext
+ exists_isRegular_tfae
+ ext_subsingleton_of_lt_moduleDepth
+ free_of_isMaximalCohenMacaulay_of_isRegularLocalRing
+ ideal_depth_quotient_regular_sequence_add_length_eq_ideal_depth
+ instance (R : Type*) [CommRing R] (I : Ideal R) [IsNoetherianRing R] :
+ instance (priority := low) [IsNoetherianRing R] [IsLocalRing R] [Small.{v} R]
+ instance : RingHomSurjective (residue R) := ⟨residue_surjective⟩
+ instance [IsCohenMacaulayLocalRing R] : (ModuleCat.of R R).IsCohenMacaulay
+ instance [IsRegularLocalRing R] : IsDomain R := isDomain_of_isRegularLocalRing R
+ isCohenMacaulayLocalRing_def
+ isCohenMacaulayLocalRing_iff
+ isCohenMacaulayLocalRing_localization_atPrime
+ isCohenMacaulayLocalRing_of_isRegularLocalRing
+ isCohenMacaulayLocalRing_of_ringEquiv
+ isCohenMacaulayLocalRing_of_ringKrullDim_le_depth
+ isCohenMacaulayRing_def
+ isCohenMacaulayRing_def'
+ isCohenMacaulayRing_iff
+ isCohenMacaulayRing_of_ringEquiv
+ isCohenMacaulay_of_isMaximalCohenMacaulay
+ isDomain_of_isRegularLocalRing
+ isField_of_isRegularLocalRing_of_dimension_zero
+ isLocalization_at_prime_prime_depth_le_depth
+ isLocalize_at_prime_depth_eq_of_isCohenMacaulay
+ isLocalize_at_prime_dim_eq_prime_depth_of_isCohenMacaulay
+ isLocalize_at_prime_isCohenMacaulay_of_isCohenMacaulay
+ isLocalizedModule_quotSMulTopIsLocalizedModuleMap
+ isMaximalCohenMacaulay_def
+ isRegular_of_span_eq_maximalIdeal
+ moduleDepth
+ moduleDepth_eq_depth_of_supp_eq
+ moduleDepth_eq_find
+ moduleDepth_eq_iff
+ moduleDepth_eq_of_iso_fst
+ moduleDepth_eq_of_iso_snd
+ moduleDepth_eq_of_linearEquiv
+ moduleDepth_eq_sSup_length_regular
+ moduleDepth_eq_sup_nat
+ moduleDepth_eq_top_iff
+ moduleDepth_eq_zero_of_hom_nontrivial
+ moduleDepth_ge_depth_sub_dim
+ moduleDepth_ge_min_of_shortExact_fst_fst
+ moduleDepth_ge_min_of_shortExact_fst_snd
+ moduleDepth_ge_min_of_shortExact_snd_fst
+ moduleDepth_ge_min_of_shortExact_snd_snd
+ moduleDepth_ge_min_of_shortExact_trd_fst
+ moduleDepth_ge_min_of_shortExact_trd_snd
+ moduleDepth_lt_top_iff
+ moduleDepth_quotSMulTop_succ_eq_moduleDepth
+ moduleDepth_quotient_regular_sequence_add_length_eq_moduleDepth
+ quotSMulTopIsLocalizedModuleMap
+ quotSMulTop_isCohenMacaulay_iff_isCohenMacaulay
+ quotient_isRegularLocalRing_tfae
+ quotient_prime_ringKrullDim_ne_bot
+ quotient_regular_isCohenMacaulay_iff_isCohenMacaulay
+ quotient_regular_sequence_isCohenMacaulay_iff_isCohenMacaulay
+ quotient_regular_smul_top_isCohenMacaulay_iff_isCohenMacaulay
+ quotient_span_regular_isCohenMacaulay_iff_isCohenMacaulay
+ quotient_span_singleton
+ ring_depth_shrink_eq
+ smul_top_quotSMulTop_ne_top_of_smul_top_ne_top
+ spanFinrank_eq_one_iff
+ subset_iUnion_iff_mem_of_isMaximal_of_finite
+ subsingleton_ext_of_exists_isRegular
+ toCotangentSpace

You can run this locally as follows
## from your `mathlib4` directory:
git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci

## summary with just the declaration names:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh <optional_commit>

## more verbose report:
../mathlib-ci/scripts/pr_summary/declarations_diff.sh long <optional_commit>

The doc-module for scripts/pr_summary/declarations_diff.sh in the mathlib-ci repository contains some details about this script.

Declarations diff (Lean)

Lean-aware diff — post-build, computed from the Lean environment (commit b4d49cf).

  • +136 new declarations
  • −0 removed declarations
+FiniteRingKrullDim.ringKrullDim_eq_nat
+Ideal.depth
+Ideal.depth.congr_simp
+Ideal.depth_eq_of_iso
+Ideal.depth_eq_of_linearEquiv
+Ideal.depth_eq_top_of_subsingleton
+Ideal.depth_quotSMulTop_succ_eq_moduleDepth
+Ideal.span_singleton_mul_eq_self_of_isPrime
+Ideal.subset_iUnion_iff_mem_of_isMaximal_of_finite
+IsCohenMacaulayLocalRing
+IsCohenMacaulayLocalRing.casesOn
+IsCohenMacaulayLocalRing.depth_eq_dim
+IsCohenMacaulayLocalRing.mk
+IsCohenMacaulayLocalRing.of_isLocalRing_of_isCohenMacaulayRing
+IsCohenMacaulayLocalRing.rec
+IsCohenMacaulayLocalRing.recOn
+IsCohenMacaulayLocalRing.toIsLocalRing
+IsCohenMacaulayRing
+IsCohenMacaulayRing.CM_localize
+IsCohenMacaulayRing.casesOn
+IsCohenMacaulayRing.mk
+IsCohenMacaulayRing.of_isCohenMacaulayLocalRing
+IsCohenMacaulayRing.rec
+IsCohenMacaulayRing.recOn
+IsDiscreteValuationRing.of_isRegularLocalRing_of_ringKrullDim_eq_one
+IsLocalRing.CotangentSpace.congr_simp
+IsLocalRing.depth
+IsLocalRing.depth.congr_simp
+IsLocalRing.depth_eq_of_algebraMap_surjective
+IsLocalRing.depth_eq_of_iso
+IsLocalRing.depth_eq_of_linearEquiv
+IsLocalRing.depth_eq_of_ringEquiv
+IsLocalRing.depth_eq_sSup_length_regular
+IsLocalRing.depth_eq_top_of_subsingleton
+IsLocalRing.depth_quotSMulTop_succ_eq_moduleDepth
+IsLocalRing.depth_quotient_regular_sequence_add_length_eq_depth
+IsLocalRing.depth_quotient_regular_succ_eq_depth
+IsLocalRing.depth_quotient_span_regular_succ_eq_depth
+IsLocalRing.ideal_depth_eq_sSup_length_regular
+IsLocalRing.ideal_depth_le_depth
+IsLocalRing.instRingHomSurjectiveResidueFieldResidue
+IsLocalRing.spanFinrank_maximalIdeal_add_finrank_eq_of_surjective
+IsLocalRing.spanFinrank_maximalIdeal_quotient
+IsLocalRing.toCotangentSpace
+LinearMapOfSemiLinearMapAlgebraMap
+ModuleCat.IsCohenMacaulay
+ModuleCat.IsCohenMacaulay.casesOn
+ModuleCat.IsCohenMacaulay.congr_simp
+ModuleCat.IsCohenMacaulay.depth_eq_dim
+ModuleCat.IsCohenMacaulay.mk
+ModuleCat.IsCohenMacaulay.rec
+ModuleCat.IsCohenMacaulay.recOn
+ModuleCat.IsCohenMacaulay_of_iso
+ModuleCat.IsMaximalCohenMacaulay
+ModuleCat.IsMaximalCohenMacaulay.casesOn
+ModuleCat.IsMaximalCohenMacaulay.depth_eq_dim
+ModuleCat.IsMaximalCohenMacaulay.mk
+ModuleCat.IsMaximalCohenMacaulay.rec
+ModuleCat.IsMaximalCohenMacaulay.recOn
+ModuleCat.depth_eq_supportDim_of_cohenMacaulay
+ModuleCat.depth_eq_supportDim_unbot_of_cohenMacaulay
+ModuleCat.exists_isRegular_of_exists_subsingleton_ext
+ModuleCat.exists_isRegular_tfae
+ModuleCat.isCohenMacaulay_iff
+ModuleCat.subsingleton_ext_of_exists_isRegular
+SemiLinearMapAlgebraMapOfLinearMap
+SemiLinearMapAlgebraMapOfLinearMap.congr_simp
+Submodule.comap_lt_top_of_lt_range
+Submodule.spanFinrank_eq_one_iff
+associatedPrimes_self_eq_minimalPrimes
+associated_prime_eq_minimalPrimes_isCohenMacaulay
+associated_prime_minimal_of_isCohenMacaulay
+depth_eq_dim_quotient_associated_prime_of_isCohenMacaulay
+depth_le_ringKrullDim
+depth_le_ringKrullDim_associatedPrime
+depth_le_supportDim
+depth_ne_top
+depth_quotient_regular_sequence_add_length_eq_depth
+ext_subsingleton_of_lt_moduleDepth
+free_of_isMaximalCohenMacaulay_of_isRegularLocalRing
+ideal_depth_quotient_regular_sequence_add_length_eq_ideal_depth
+instIsCohenMacaulayOf
+instIsDomainOfIsRegularLocalRing
+instNontrivialCarrierOfIsNoetherianRingOfIsMaximalCohenMacaulay
+isCohenMacaulayLocalRing_def
+isCohenMacaulayLocalRing_iff
+isCohenMacaulayLocalRing_localization_atPrime
+isCohenMacaulayLocalRing_of_isRegularLocalRing
+isCohenMacaulayLocalRing_of_ringEquiv
+isCohenMacaulayLocalRing_of_ringKrullDim_le_depth
+isCohenMacaulayRing_def
+isCohenMacaulayRing_def'
+isCohenMacaulayRing_iff
+isCohenMacaulayRing_of_ringEquiv
+isCohenMacaulay_of_isMaximalCohenMacaulay
+isDomain_of_isRegularLocalRing
+isField_of_isRegularLocalRing_of_dimension_zero
+isLocalization_at_prime_prime_depth_le_depth
+isLocalize_at_prime_depth_eq_of_isCohenMacaulay
+isLocalize_at_prime_dim_eq_prime_depth_of_isCohenMacaulay
+isLocalize_at_prime_isCohenMacaulay_of_isCohenMacaulay
+isLocalizedModule_quotSMulTopIsLocalizedModuleMap
+isMaximalCohenMacaulay_def
+isRegular_of_span_eq_maximalIdeal
+moduleDepth
+moduleDepth.congr_simp
+moduleDepth_eq_depth_of_supp_eq
+moduleDepth_eq_find
+moduleDepth_eq_iff
+moduleDepth_eq_of_iso_fst
+moduleDepth_eq_of_iso_snd
+moduleDepth_eq_of_linearEquiv
+moduleDepth_eq_sSup_length_regular
+moduleDepth_eq_sup_nat
+moduleDepth_eq_top_iff
+moduleDepth_eq_zero_of_hom_nontrivial
+moduleDepth_ge_depth_sub_dim
+moduleDepth_ge_min_of_shortExact_fst_fst
+moduleDepth_ge_min_of_shortExact_fst_snd
+moduleDepth_ge_min_of_shortExact_snd_fst
+moduleDepth_ge_min_of_shortExact_snd_snd
+moduleDepth_ge_min_of_shortExact_trd_fst
+moduleDepth_ge_min_of_shortExact_trd_snd
+moduleDepth_lt_top_iff
+moduleDepth_quotSMulTop_succ_eq_moduleDepth
+moduleDepth_quotient_regular_sequence_add_length_eq_moduleDepth
+quotSMulTopIsLocalizedModuleMap
+quotSMulTop_isCohenMacaulay_iff_isCohenMacaulay
+quotient_isRegularLocalRing_tfae
+quotient_prime_ringKrullDim_ne_bot
+quotient_regular_isCohenMacaulay_iff_isCohenMacaulay
+quotient_regular_sequence_isCohenMacaulay_iff_isCohenMacaulay
+quotient_regular_smul_top_isCohenMacaulay_iff_isCohenMacaulay
+quotient_span_regular_isCohenMacaulay_iff_isCohenMacaulay
+quotient_span_singleton
+ring_depth_shrink_eq

Increase in strong tech debt: (relative, absolute) = (7.00, 0.00)
Current number Change Type (strong)
5672 7 backward.isDefEq.respectTransparency
Increase in weak tech debt: (relative, absolute) = (3.00, 0.00)
Current number Change Type (weak)
4958 3 exposed public sections

Current commit b4d49cfc19
Reference commit 07f4b8dcd0

This script lives in the mathlib-ci repository. To run it locally, from your mathlib4 directory:

git clone https://github.com/leanprover-community/mathlib-ci.git ../mathlib-ci
../mathlib-ci/scripts/reporting/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).

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