Homogeneous Localization #
Notation #
ฮนis a commutative monoid;Ris a commutative semiring;Ais a commutative ring and anR-algebra;๐ : ฮน โ Submodule R Ais the grading ofA;x : Submonoid Ais a submonoid
Main definitions and results #
This file constructs the subring of Aโ where the numerator and denominator have the same grading,
i.e. {a/b โ Aโ | โ (i : ฮน), a โ ๐แตข โง b โ ๐แตข}.
HomogeneousLocalization.NumDenSameDeg: a structure with a numerator and denominator field where they are required to have the same grading.
However NumDenSameDeg ๐ x cannot have a ring structure for many reasons, for example if c
is a NumDenSameDeg, then generally, c + (-c) is not necessarily 0 for degree reasons ---
0 is considered to have grade zero (see deg_zero) but c + (-c) has the same degree as c. To
circumvent this, we quotient NumDenSameDeg ๐ x by the kernel of c โฆ c.num / c.den.
-
HomogeneousLocalization.NumDenSameDeg.embedding: forx : Submonoid Aand anyc : NumDenSameDeg ๐ x, or equivalent a numerator and a denominator of the same degree, we get an elementc.num / c.denofAโ. -
HomogeneousLocalization:NumDenSameDeg ๐ xquotiented by kernel ofembedding ๐ x. -
HomogeneousLocalization.val: iff : HomogeneousLocalization ๐ x, thenf.valis an element ofAโ. In another word, one can viewHomogeneousLocalization ๐ xas a subring ofAโthroughHomogeneousLocalization.val. -
HomogeneousLocalization.num: iff : HomogeneousLocalization ๐ x, thenf.num : Ais the numerator off. -
HomogeneousLocalization.den: iff : HomogeneousLocalization ๐ x, thenf.den : Ais the denominator off. -
HomogeneousLocalization.deg: iff : HomogeneousLocalization ๐ x, thenf.deg : ฮนis the degree offsuch thatf.num โ ๐ f.degandf.den โ ๐ f.deg(seeHomogeneousLocalization.num_mem_degandHomogeneousLocalization.den_mem_deg). -
HomogeneousLocalization.num_mem_deg: iff : HomogeneousLocalization ๐ x, thenf.num_mem_degis a proof thatf.num โ ๐ f.deg. -
HomogeneousLocalization.den_mem_deg: iff : HomogeneousLocalization ๐ x, thenf.den_mem_degis a proof thatf.den โ ๐ f.deg. -
HomogeneousLocalization.eq_num_div_den: iff : HomogeneousLocalization ๐ x, thenf.val : Aโis equal tof.num / f.den. -
HomogeneousLocalization.localRing:HomogeneousLocalization ๐ xis a local ring whenxis the complement of some prime ideals.
References #
- [Robin Hartshorne, Algebraic Geometry][Har77]
Let x be a submonoid of A, then NumDenSameDeg ๐ x is a structure with a numerator and a
denominator with same grading such that the denominator is contained in x.
- deg : ฮน
- num : โฅ(๐ self.deg)
- den : โฅ(๐ self.deg)
- den_mem : โself.den โ x
Instances For
Equations
- HomogeneousLocalization.NumDenSameDeg.instOneNumDenSameDeg x = { one := { deg := 0, num := { val := 1, property := โฏ }, den := { val := 1, property := โฏ }, den_mem := โฏ } }
Equations
- HomogeneousLocalization.NumDenSameDeg.instZeroNumDenSameDeg x = { zero := { deg := 0, num := 0, den := { val := 1, property := โฏ }, den_mem := โฏ } }
Equations
- One or more equations did not get rendered due to their size.
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For x : prime ideal of A and any p : NumDenSameDeg ๐ x, or equivalent a numerator and a
denominator of the same degree, we get an element p.num / p.den of Aโ.
Equations
- HomogeneousLocalization.NumDenSameDeg.embedding ๐ x p = Localization.mk โp.num { val := โp.den, property := โฏ }
Instances For
For x : prime ideal of A, HomogeneousLocalization ๐ x is NumDenSameDeg ๐ x modulo the
kernel of embedding ๐ x. This is essentially the subring of Aโ where the numerator and
denominator share the same grading.
Equations
Instances For
View an element of HomogeneousLocalization ๐ x as an element of Aโ by forgetting that the
numerator and denominator are of the same grading.
Equations
Instances For
Equations
- HomogeneousLocalization.hasPow x = { pow := fun (z : HomogeneousLocalization ๐ x) (n : โ) => Quotient.map' (fun (x_1 : HomogeneousLocalization.NumDenSameDeg ๐ x) => x_1 ^ n) โฏ z }
Equations
- HomogeneousLocalization.instSMulHomogeneousLocalization x = { smul := fun (m : ฮฑ) => Quotient.map' (fun (x_1 : HomogeneousLocalization.NumDenSameDeg ๐ x) => m โข x_1) โฏ }
Equations
- HomogeneousLocalization.instNegHomogeneousLocalization x = { neg := Quotient.map' Neg.neg โฏ }
Equations
- HomogeneousLocalization.instAddHomogeneousLocalization x = { add := Quotient.mapโ' (fun (x_1 x_2 : HomogeneousLocalization.NumDenSameDeg ๐ x) => x_1 + x_2) โฏ }
Equations
- HomogeneousLocalization.instSubHomogeneousLocalization x = { sub := fun (z1 z2 : HomogeneousLocalization ๐ x) => z1 + -z2 }
Equations
- HomogeneousLocalization.instMulHomogeneousLocalization x = { mul := Quotient.mapโ' (fun (x_1 x_2 : HomogeneousLocalization.NumDenSameDeg ๐ x) => x_1 * x_2) โฏ }
Equations
- HomogeneousLocalization.instOneHomogeneousLocalization x = { one := Quotient.mk'' 1 }
Equations
- HomogeneousLocalization.instZeroHomogeneousLocalization x = { zero := Quotient.mk'' 0 }
Equations
- HomogeneousLocalization.instNatCastHomogeneousLocalization = { natCast := Nat.unaryCast }
Equations
- HomogeneousLocalization.instIntCastHomogeneousLocalization = { intCast := Int.castDef }
Equations
- HomogeneousLocalization.homogenousLocalizationCommRing = Function.Injective.commRing HomogeneousLocalization.val โฏ โฏ โฏ โฏ โฏ โฏ โฏ โฏ โฏ โฏ โฏ โฏ
Equations
- One or more equations did not get rendered due to their size.
Numerator of an element in HomogeneousLocalization x.
Equations
- HomogeneousLocalization.num f = โ(Quotient.out' f).num
Instances For
Denominator of an element in HomogeneousLocalization x.
Equations
- HomogeneousLocalization.den f = โ(Quotient.out' f).den
Instances For
For an element in HomogeneousLocalization x, degree is the natural number i such that
๐ i contains both numerator and denominator.
Equations
- HomogeneousLocalization.deg f = (Quotient.out' f).deg
Instances For
Localizing a ring homogeneously at a prime ideal.
Equations
- HomogeneousLocalization.AtPrime ๐ ๐ญ = HomogeneousLocalization ๐ (Ideal.primeCompl ๐ญ)
Instances For
Equations
- โฏ = โฏ
Equations
- โฏ = โฏ
Localizing away from powers of f homogeneously.
Equations
- HomogeneousLocalization.Away ๐ f = HomogeneousLocalization ๐ (Submonoid.powers f)