Documentation

Mathlib.Algebra.RingQuot

Quotients of semirings #

In this file, we directly define the quotient of a semiring by any relation, by building a bigger relation that represents the ideal generated by that relation.

We prove the universal properties of the quotient, and recommend avoiding relying on the actual definition, which is made irreducible for this purpose.

Since everything runs in parallel for quotients of R-algebras, we do that case at the same time.

instance RingCon.instAlgebraQuotient {S : Type uS} [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] (c : RingCon A) :

Algebra S c.Quotient

Equations

@[simp]

theorem RingCon.coe_algebraMap {S : Type uS} [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] (c : RingCon A) (s : S) :

↑((algebraMap S A) s) = (algebraMap S c.Quotient) s

inductive RingQuot.Rel {R : Type uR} [Semiring R] (r : R → R → Prop) :

R → R → Prop

Given an arbitrary relation r on a ring, we strengthen it to a relation Rel r, such that the equivalence relation generated by Rel r has x ~ y if and only if x - y is in the ideal generated by elements a - b such that r a b.

of {R : Type uR} [Semiring R] {r : R → R → Prop} ⦃x y : R⦄ (h : r x y) : Rel r x y
add_left {R : Type uR} [Semiring R] {r : R → R → Prop} ⦃a b c : R⦄ : Rel r a b → Rel r (a + c) (b + c)
mul_left {R : Type uR} [Semiring R] {r : R → R → Prop} ⦃a b c : R⦄ : Rel r a b → Rel r (a * c) (b * c)
mul_right {R : Type uR} [Semiring R] {r : R → R → Prop} ⦃a b c : R⦄ : Rel r b c → Rel r (a * b) (a * c)

Instances For

theorem RingQuot.Rel.add_right {R : Type uR} [Semiring R] {r : R → R → Prop} ⦃a b c : R⦄ (h : Rel r b c) :

Rel r (a + b) (a + c)

theorem RingQuot.Rel.neg {R : Type uR} [Ring R] {r : R → R → Prop} ⦃a b : R⦄ (h : Rel r a b) :

Rel r (-a) (-b)

theorem RingQuot.Rel.sub_left {R : Type uR} [Ring R] {r : R → R → Prop} ⦃a b c : R⦄ (h : Rel r a b) :

Rel r (a - c) (b - c)

theorem RingQuot.Rel.sub_right {R : Type uR} [Ring R] {r : R → R → Prop} ⦃a b c : R⦄ (h : Rel r b c) :

Rel r (a - b) (a - c)

theorem RingQuot.Rel.smul {S : Type uS} [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] {r : A → A → Prop} (k : S) ⦃a b : A⦄ (h : Rel r a b) :

Rel r (k • a) (k • b)

def RingQuot.ringCon {R : Type uR} [Semiring R] (r : R → R → Prop) :

EqvGen (RingQuot.Rel r) is a ring congruence.

Equations

Instances For

theorem RingQuot.eqvGen_rel_eq {R : Type uR} [Semiring R] (r : R → R → Prop) :

Relation.EqvGen (Rel r) = RingConGen.Rel r

structure RingQuot {R : Type uR} [Semiring R] (r : R → R → Prop) :

The quotient of a ring by an arbitrary relation.

toQuot : Quot (Rel r)

Instances For

instance RingQuot.instNatCast {R : Type uR} [Semiring R] (r : R → R → Prop) :

NatCast (RingQuot r)

Equations

instance RingQuot.instZero {R : Type uR} [Semiring R] (r : R → R → Prop) :

Zero (RingQuot r)

Equations

instance RingQuot.instOne {R : Type uR} [Semiring R] (r : R → R → Prop) :

One (RingQuot r)

Equations

instance RingQuot.instAdd {R : Type uR} [Semiring R] (r : R → R → Prop) :

Add (RingQuot r)

Equations

instance RingQuot.instMul {R : Type uR} [Semiring R] (r : R → R → Prop) :

Mul (RingQuot r)

Equations

instance RingQuot.instNatPow {R : Type uR} [Semiring R] (r : R → R → Prop) :

NatPow (RingQuot r)

Equations

instance RingQuot.instNeg {R : Type uR} [Ring R] (r : R → R → Prop) :

Neg (RingQuot r)

Equations

instance RingQuot.instSub {R : Type uR} [Ring R] (r : R → R → Prop) :

Sub (RingQuot r)

Equations

instance RingQuot.instSMulOfAlgebra {R : Type uR} [Semiring R] {S : Type uS} [CommSemiring S] (r : R → R → Prop) [Algebra S R] :

SMul S (RingQuot r)

Equations

theorem RingQuot.zero_quot {R : Type uR} [Semiring R] (r : R → R → Prop) :

{ toQuot := Quot.mk (Rel r) 0 } = 0

theorem RingQuot.one_quot {R : Type uR} [Semiring R] (r : R → R → Prop) :

{ toQuot := Quot.mk (Rel r) 1 } = 1

theorem RingQuot.add_quot {R : Type uR} [Semiring R] (r : R → R → Prop) {a b : R} :

{ toQuot := Quot.mk (Rel r) a } + { toQuot := Quot.mk (Rel r) b } = { toQuot := Quot.mk (Rel r) (a + b) }

theorem RingQuot.mul_quot {R : Type uR} [Semiring R] (r : R → R → Prop) {a b : R} :

{ toQuot := Quot.mk (Rel r) a } * { toQuot := Quot.mk (Rel r) b } = { toQuot := Quot.mk (Rel r) (a * b) }

theorem RingQuot.pow_quot {R : Type uR} [Semiring R] (r : R → R → Prop) {a : R} {n : ℕ} :

{ toQuot := Quot.mk (Rel r) a } ^ n = { toQuot := Quot.mk (Rel r) (a ^ n) }

theorem RingQuot.neg_quot {R : Type uR} [Ring R] (r : R → R → Prop) {a : R} :

-{ toQuot := Quot.mk (Rel r) a } = { toQuot := Quot.mk (Rel r) (-a) }

theorem RingQuot.sub_quot {R : Type uR} [Ring R] (r : R → R → Prop) {a b : R} :

{ toQuot := Quot.mk (Rel r) a } - { toQuot := Quot.mk (Rel r) b } = { toQuot := Quot.mk (Rel r) (a - b) }

theorem RingQuot.smul_quot {R : Type uR} [Semiring R] {S : Type uS} [CommSemiring S] (r : R → R → Prop) [Algebra S R] {n : S} {a : R} :

n • { toQuot := Quot.mk (Rel r) a } = { toQuot := Quot.mk (Rel r) (n • a) }

instance RingQuot.instIsScalarTower {R : Type uR} [Semiring R] {S : Type uS} [CommSemiring S] {T : Type uT} (r : R → R → Prop) [CommSemiring T] [SMul S T] [Algebra S R] [Algebra T R] [IsScalarTower S T R] :

IsScalarTower S T (RingQuot r)

instance RingQuot.instSMulCommClass {R : Type uR} [Semiring R] {S : Type uS} [CommSemiring S] {T : Type uT} (r : R → R → Prop) [CommSemiring T] [Algebra S R] [Algebra T R] [SMulCommClass S T R] :

SMulCommClass S T (RingQuot r)

instance RingQuot.instAddCommMonoid {R : Type uR} [Semiring R] (r : R → R → Prop) :

AddCommMonoid (RingQuot r)

Equations

instance RingQuot.instMonoidWithZero {R : Type uR} [Semiring R] (r : R → R → Prop) :

MonoidWithZero (RingQuot r)

Equations

instance RingQuot.instSemiring {R : Type uR} [Semiring R] (r : R → R → Prop) :

Semiring (RingQuot r)

Equations

instance RingQuot.instRing {R : Type uR} [Ring R] (r : R → R → Prop) :

Ring (RingQuot r)

Equations

instance RingQuot.instCommSemiring {R : Type uR} [CommSemiring R] (r : R → R → Prop) :

CommSemiring (RingQuot r)

Equations

instance RingQuot.instCommRing {R : Type uR} [CommRing R] (r : R → R → Prop) :

CommRing (RingQuot r)

Equations

instance RingQuot.instInhabited {R : Type uR} [Semiring R] (r : R → R → Prop) :

Inhabited (RingQuot r)

Equations

instance RingQuot.instAlgebra {R : Type uR} [Semiring R] {S : Type uS} [CommSemiring S] [Algebra S R] (r : R → R → Prop) :

Algebra S (RingQuot r)

Equations

@[irreducible]

def RingQuot.mkRingHom {R : Type u_1} [Semiring R] (r : R → R → Prop) :

R →+* RingQuot r

The quotient map from a ring to its quotient, as a homomorphism of rings.

Equations

Instances For

theorem RingQuot.mkRingHom_def {R : Type u_1} [Semiring R] (r : R → R → Prop) :

mkRingHom r = { toFun := fun (x : R) => { toQuot := Quot.mk (Rel r) x }, map_one' := ⋯, map_mul' := ⋯, map_zero' := ⋯, map_add' := ⋯ }

theorem RingQuot.mkRingHom_rel {R : Type uR} [Semiring R] {r : R → R → Prop} {x y : R} (w : r x y) :

(mkRingHom r) x = (mkRingHom r) y

theorem RingQuot.mkRingHom_surjective {R : Type uR} [Semiring R] (r : R → R → Prop) :

Function.Surjective ⇑(mkRingHom r)

theorem RingQuot.ringQuot_ext {R : Type uR} [Semiring R] {T : Type uT} [NonAssocSemiring T] {r : R → R → Prop} (f g : RingQuot r →+* T) (w : f.comp (mkRingHom r) = g.comp (mkRingHom r)) :

f = g

theorem RingQuot.ringQuot_ext_iff {R : Type uR} [Semiring R] {T : Type uT} [NonAssocSemiring T] {r : R → R → Prop} {f g : RingQuot r →+* T} :

f = g ↔ f.comp (mkRingHom r) = g.comp (mkRingHom r)

@[irreducible]

def RingQuot.preLift {R : Type u_1} [Semiring R] {T : Type u_2} [Semiring T] {r : R → R → Prop} {f : R →+* T} (h : ∀ ⦃x y : R⦄, r x y → f x = f y) :

RingQuot r →+* T

Equations

Instances For

theorem RingQuot.preLift_def {R : Type u_1} [Semiring R] {T : Type u_2} [Semiring T] {r : R → R → Prop} {f : R →+* T} (h : ∀ ⦃x y : R⦄, r x y → f x = f y) :

preLift h = { toFun := fun (x : RingQuot r) => Quot.lift ⇑f ⋯ x.toQuot, map_one' := ⋯, map_mul' := ⋯, map_zero' := ⋯, map_add' := ⋯ }

@[irreducible]

def RingQuot.lift {R : Type u_1} [Semiring R] {T : Type u_2} [Semiring T] {r : R → R → Prop} :

{ f : R →+* T // ∀ ⦃x y : R⦄, r x y → f x = f y } ≃ (RingQuot r →+* T)

Any ring homomorphism f : R →+* T which respects a relation r : R → R → Prop factors uniquely through a morphism RingQuot r →+* T.

Equations

Instances For

theorem RingQuot.lift_def {R : Type u_1} [Semiring R] {T : Type u_2} [Semiring T] {r : R → R → Prop} :

lift = { toFun := fun (f : { f : R →+* T // ∀ ⦃x y : R⦄, r x y → f x = f y }) => preLift ⋯, invFun := fun (F : RingQuot r →+* T) => ⟨F.comp (mkRingHom r), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }

@[simp]

theorem RingQuot.lift_mkRingHom_apply {R : Type uR} [Semiring R] {T : Type uT} [Semiring T] (f : R →+* T) {r : R → R → Prop} (w : ∀ ⦃x y : R⦄, r x y → f x = f y) (x : R) :

(lift ⟨f, w⟩) ((mkRingHom r) x) = f x

theorem RingQuot.lift_unique {R : Type uR} [Semiring R] {T : Type uT} [Semiring T] (f : R →+* T) {r : R → R → Prop} (w : ∀ ⦃x y : R⦄, r x y → f x = f y) (g : RingQuot r →+* T) (h : g.comp (mkRingHom r) = f) :

g = lift ⟨f, w⟩

theorem RingQuot.eq_lift_comp_mkRingHom {R : Type uR} [Semiring R] {T : Type uT} [Semiring T] {r : R → R → Prop} (f : RingQuot r →+* T) :

f = lift ⟨f.comp (mkRingHom r), ⋯⟩

We now verify that in the case of a commutative ring, the RingQuot construction agrees with the quotient by the appropriate ideal.

def RingQuot.ringQuotToIdealQuotient {B : Type uR} [CommRing B] (r : B → B → Prop) :

RingQuot r →+* B ⧸ Ideal.ofRel r

The universal ring homomorphism from RingQuot r to B ⧸ Ideal.ofRel r.

Equations

Instances For

@[simp]

theorem RingQuot.ringQuotToIdealQuotient_apply {B : Type uR} [CommRing B] (r : B → B → Prop) (x : B) :

(ringQuotToIdealQuotient r) ((mkRingHom r) x) = (Ideal.Quotient.mk (Ideal.ofRel r)) x

def RingQuot.idealQuotientToRingQuot {B : Type uR} [CommRing B] (r : B → B → Prop) :

B ⧸ Ideal.ofRel r →+* RingQuot r

The universal ring homomorphism from B ⧸ Ideal.ofRel r to RingQuot r.

Equations

Instances For

@[simp]

theorem RingQuot.idealQuotientToRingQuot_apply {B : Type uR} [CommRing B] (r : B → B → Prop) (x : B) :

(idealQuotientToRingQuot r) ((Ideal.Quotient.mk (Ideal.ofRel r)) x) = (mkRingHom r) x

def RingQuot.ringQuotEquivIdealQuotient {B : Type uR} [CommRing B] (r : B → B → Prop) :

RingQuot r ≃+* B ⧸ Ideal.ofRel r

The ring equivalence between RingQuot r and (Ideal.ofRel r).quotient

Equations

Instances For

theorem RingQuot.mkAlgHom_def (S : Type u_1) [CommSemiring S] {A : Type u_2} [Semiring A] [Algebra S A] (s : A → A → Prop) :

mkAlgHom S s = let __src := mkRingHom s; { toRingHom := __src, commutes' := ⋯ }

@[irreducible]

def RingQuot.mkAlgHom (S : Type u_1) [CommSemiring S] {A : Type u_2} [Semiring A] [Algebra S A] (s : A → A → Prop) :

A →ₐ[S] RingQuot s

The quotient map from an S-algebra to its quotient, as a homomorphism of S-algebras.

Equations

Instances For

@[simp]

theorem RingQuot.mkAlgHom_coe (S : Type uS) [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] (s : A → A → Prop) :

↑(mkAlgHom S s) = mkRingHom s

theorem RingQuot.mkAlgHom_rel (S : Type uS) [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] {s : A → A → Prop} {x y : A} (w : s x y) :

(mkAlgHom S s) x = (mkAlgHom S s) y

theorem RingQuot.mkAlgHom_surjective (S : Type uS) [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] (s : A → A → Prop) :

Function.Surjective ⇑(mkAlgHom S s)

theorem RingQuot.ringQuot_ext' (S : Type uS) [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] {B : Type u₄} [Semiring B] [Algebra S B] {s : A → A → Prop} (f g : RingQuot s →ₐ[S] B) (w : f.comp (mkAlgHom S s) = g.comp (mkAlgHom S s)) :

f = g

theorem RingQuot.ringQuot_ext'_iff {S : Type uS} [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] {B : Type u₄} [Semiring B] [Algebra S B] {s : A → A → Prop} {f g : RingQuot s →ₐ[S] B} :

f = g ↔ f.comp (mkAlgHom S s) = g.comp (mkAlgHom S s)

theorem RingQuot.preLiftAlgHom_def (S : Type u_1) [CommSemiring S] {A : Type u_2} [Semiring A] [Algebra S A] {B : Type u_3} [Semiring B] [Algebra S B] {s : A → A → Prop} {f : A →ₐ[S] B} (h : ∀ ⦃x y : A⦄, s x y → f x = f y) :

preLiftAlgHom S h = { toFun := fun (x : RingQuot s) => Quot.lift ⇑f ⋯ x.toQuot, map_one' := ⋯, map_mul' := ⋯, map_zero' := ⋯, map_add' := ⋯, commutes' := ⋯ }

@[irreducible]

def RingQuot.preLiftAlgHom (S : Type u_1) [CommSemiring S] {A : Type u_2} [Semiring A] [Algebra S A] {B : Type u_3} [Semiring B] [Algebra S B] {s : A → A → Prop} {f : A →ₐ[S] B} (h : ∀ ⦃x y : A⦄, s x y → f x = f y) :

RingQuot s →ₐ[S] B

Equations

Instances For

theorem RingQuot.liftAlgHom_def (S : Type u_1) [CommSemiring S] {A : Type u_2} [Semiring A] [Algebra S A] {B : Type u_3} [Semiring B] [Algebra S B] {s : A → A → Prop} :

liftAlgHom S = { toFun := fun (f' : { f : A →ₐ[S] B // ∀ ⦃x y : A⦄, s x y → f x = f y }) => preLiftAlgHom S ⋯, invFun := fun (F : RingQuot s →ₐ[S] B) => ⟨F.comp (mkAlgHom S s), ⋯⟩, left_inv := ⋯, right_inv := ⋯ }

@[irreducible]

def RingQuot.liftAlgHom (S : Type u_1) [CommSemiring S] {A : Type u_2} [Semiring A] [Algebra S A] {B : Type u_3} [Semiring B] [Algebra S B] {s : A → A → Prop} :

{ f : A →ₐ[S] B // ∀ ⦃x y : A⦄, s x y → f x = f y } ≃ (RingQuot s →ₐ[S] B)

Any S-algebra homomorphism f : A →ₐ[S] B which respects a relation s : A → A → Prop factors uniquely through a morphism RingQuot s →ₐ[S] B.

Equations

Instances For

@[simp]

theorem RingQuot.liftAlgHom_mkAlgHom_apply (S : Type uS) [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] {B : Type u₄} [Semiring B] [Algebra S B] (f : A →ₐ[S] B) {s : A → A → Prop} (w : ∀ ⦃x y : A⦄, s x y → f x = f y) (x : A) :

((liftAlgHom S) ⟨f, w⟩) ((mkAlgHom S s) x) = f x

theorem RingQuot.liftAlgHom_unique (S : Type uS) [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] {B : Type u₄} [Semiring B] [Algebra S B] (f : A →ₐ[S] B) {s : A → A → Prop} (w : ∀ ⦃x y : A⦄, s x y → f x = f y) (g : RingQuot s →ₐ[S] B) (h : g.comp (mkAlgHom S s) = f) :

g = (liftAlgHom S) ⟨f, w⟩

theorem RingQuot.eq_liftAlgHom_comp_mkAlgHom (S : Type uS) [CommSemiring S] {A : Type uA} [Semiring A] [Algebra S A] {B : Type u₄} [Semiring B] [Algebra S B] {s : A → A → Prop} (f : RingQuot s →ₐ[S] B) :

f = (liftAlgHom S) ⟨f.comp (mkAlgHom S s), ⋯⟩