Ideals in localizations of commutative rings

Implementation notes

See Mathlib/RingTheory/Localization/Basic.lean for a design overview.

Tags

localization, ring localization, commutative ring localization, characteristic predicate, commutative ring, field of fractions

theorem IsLocalization.mem_map_algebraMap_iff {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] {I : Ideal R} {z : S} : z ∈ Ideal.map (algebraMap R S) I ↔ ∃ (x : ↥I × ↥M), z * (algebraMap R S) ↑x.2 = (algebraMap R S) ↑x.1

theorem IsLocalization.mk'_mem_map_algebraMap_iff {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] (I : Ideal R) (x : R) (s : ↥M) : IsLocalization.mk' S x s ∈ Ideal.map (algebraMap R S) I ↔ ∃ s ∈ M, s * x ∈ I

theorem IsLocalization.map_comap {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] (J : Ideal S) : Ideal.map (algebraMap R S) (Ideal.comap (algebraMap R S) J) = J

theorem IsLocalization.comap_map_of_isPrime_disjoint {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] (I : Ideal R) (hI : I.IsPrime) (hM : Disjoint ↑M ↑I) : Ideal.comap (algebraMap R S) (Ideal.map (algebraMap R S) I) = I

def IsLocalization.orderEmbedding {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] : Ideal S ↪o Ideal R

If S is the localization of R at a submonoid, the ordering of ideals of S is embedded in the ordering of ideals of R.

Equations

• IsLocalization.orderEmbedding M S = { toFun := fun (J : Ideal S) => Ideal.comap (algebraMap R S) J, inj' := ⋯, map_rel_iff' := ⋯ }

theorem IsLocalization.isPrime_iff_isPrime_disjoint {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] (J : Ideal S) : J.IsPrime ↔ (Ideal.comap (algebraMap R S) J).IsPrime ∧ Disjoint ↑M ↑(Ideal.comap (algebraMap R S) J)

If R is a ring, then prime ideals in the localization at M correspond to prime ideals in the original ring R that are disjoint from M. This lemma gives the particular case for an ideal and its comap, see le_rel_iso_of_prime for the more general relation isomorphism

theorem IsLocalization.isPrime_of_isPrime_disjoint {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] (I : Ideal R) (hp : I.IsPrime) (hd : Disjoint ↑M ↑I) : (Ideal.map (algebraMap R S) I).IsPrime

If R is a ring, then prime ideals in the localization at M correspond to prime ideals in the original ring R that are disjoint from M. This lemma gives the particular case for an ideal and its map, see le_rel_iso_of_prime for the more general relation isomorphism, and the reverse implication

def IsLocalization.orderIsoOfPrime {R : Type u_1} [CommSemiring R] (M : Submonoid R) (S : Type u_2) [CommSemiring S] [Algebra R S] [IsLocalization M S] : { p : Ideal S // p.IsPrime } ≃o { p : Ideal R // p.IsPrime ∧ Disjoint ↑M ↑p }

If R is a ring, then prime ideals in the localization at M correspond to prime ideals in the original ring R that are disjoint from M

Equations

• One or more equations did not get rendered due to their size.

theorem IsLocalization.surjective_quotientMap_of_maximal_of_localization {R : Type u_1} [CommRing R] (M : Submonoid R) (S : Type u_2) [CommRing S] [Algebra R S] [IsLocalization M S] {I : Ideal S} [I.IsPrime] {J : Ideal R} {H : J ≤ Ideal.comap (algebraMap R S) I} (hI : (Ideal.comap (algebraMap R S) I).IsMaximal) : Function.Surjective ⇑(Ideal.quotientMap I (algebraMap R S) H)

quotientMap applied to maximal ideals of a localization is surjective. The quotient by a maximal ideal is a field, so inverses to elements already exist, and the localization necessarily maps the equivalence class of the inverse in the localization

theorem IsLocalization.bot_lt_comap_prime {R : Type u_1} [CommRing R] (M : Submonoid R) (S : Type u_2) [CommRing S] [Algebra R S] [IsLocalization M S] [IsDomain R] (hM : M ≤ nonZeroDivisors R) (p : Ideal S) [hpp : p.IsPrime] (hp0 : p ≠ ⊥) : ⊥ < Ideal.comap (algebraMap R S) p

theorem IsLocalization.ideal_eq_iInf_comap_map_away {R : Type u_1} [CommRing R] {S : Finset R} (hS : Ideal.span ↑S = ⊤) (I : Ideal R) : I = ⨅ f ∈ S, Ideal.comap (algebraMap R (Localization.Away f)) (Ideal.map (algebraMap R (Localization.Away f)) I)