Trivial Square-Zero Extension

Given a ring R together with an (R, R)-bimodule M, the trivial square-zero extension of M over R is defined to be the R-algebra R ⊕ M with multiplication given by (r₁ + m₁) * (r₂ + m₂) = r₁ r₂ + r₁ m₂ + m₁ r₂.

It is a square-zero extension because M^2 = 0.

Note that expressing this requires bimodules; we write these in general for a not-necessarily-commutative R as:

variables {R M : Type*} [Semiring R] [AddCommMonoid M]
variables [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M]

If we instead work with a commutative R' acting symmetrically on M, we write

variables {R' M : Type*} [CommSemiring R'] [AddCommMonoid M]
variables [Module R' M] [Module R'ᵐᵒᵖ M] [IsCentralScalar R' M]

noting that in this context IsCentralScalar R' M implies SMulCommClass R' R'ᵐᵒᵖ M.

Many of the later results in this file are only stated for the commutative R' for simplicity.

Main definitions

• TrivSqZeroExt.inl, TrivSqZeroExt.inr: the canonical inclusions into TrivSqZeroExt R M.
• TrivSqZeroExt.fst, TrivSqZeroExt.snd: the canonical projections from TrivSqZeroExt R M.
• triv_sq_zero_ext.algebra: the associated R-algebra structure.
• TrivSqZeroExt.lift: the universal property of the trivial square-zero extension; algebra morphisms TrivSqZeroExt R M →ₐ[S] A are uniquely defined by an algebra morphism f : R →ₐ[S] A on R and a linear map g : M →ₗ[S] A on M such that:
  • g x * g y = 0: the elements of M continue to square to zero.
  • g (r • x) = f r * g x and g (op r • x) = g x * f r: left and right actions are preserved by g.
• TrivSqZeroExt.lift: the universal property of the trivial square-zero extension; algebra morphisms TrivSqZeroExt R M →ₐ[R] A are uniquely defined by linear maps M →ₗ[R] A for which the product of any two elements in the range is zero.

def TrivSqZeroExt (R : Type u) (M : Type v) : Type (max u v)

"Trivial Square-Zero Extension".

Given a module M over a ring R, the trivial square-zero extension of M over R is defined to be the R-algebra R × M with multiplication given by (r₁ + m₁) * (r₂ + m₂) = r₁ r₂ + r₁ m₂ + r₂ m₁.

It is a square-zero extension because M^2 = 0.

Equations

• TrivSqZeroExt R M = (R × M)

def TrivSqZeroExt.inl {R : Type u} {M : Type v} [Zero M] (r : R) : TrivSqZeroExt R M

The canonical inclusion R → TrivSqZeroExt R M.

Equations

• TrivSqZeroExt.inl r = (r, 0)

def TrivSqZeroExt.inr {R : Type u} {M : Type v} [Zero R] (m : M) : TrivSqZeroExt R M

The canonical inclusion M → TrivSqZeroExt R M.

Equations

• TrivSqZeroExt.inr m = (0, m)

def TrivSqZeroExt.fst {R : Type u} {M : Type v} (x : TrivSqZeroExt R M) : R

The canonical projection TrivSqZeroExt R M → R.

Equations

• TrivSqZeroExt.fst x = x.1

def TrivSqZeroExt.snd {R : Type u} {M : Type v} (x : TrivSqZeroExt R M) : M

The canonical projection TrivSqZeroExt R M → M.

Equations

• TrivSqZeroExt.snd x = x.2

@[simp]

theorem TrivSqZeroExt.fst_mk {R : Type u} {M : Type v} (r : R) (m : M) : TrivSqZeroExt.fst (r, m) = r

@[simp]

theorem TrivSqZeroExt.snd_mk {R : Type u} {M : Type v} (r : R) (m : M) : TrivSqZeroExt.snd (r, m) = m

theorem TrivSqZeroExt.ext {R : Type u} {M : Type v} {x : TrivSqZeroExt R M} {y : TrivSqZeroExt R M} (h1 : TrivSqZeroExt.fst x = TrivSqZeroExt.fst y) (h2 : TrivSqZeroExt.snd x = TrivSqZeroExt.snd y) : x = y

@[simp]

theorem TrivSqZeroExt.fst_inl {R : Type u} (M : Type v) [Zero M] (r : R) : TrivSqZeroExt.fst (TrivSqZeroExt.inl r) = r

@[simp]

theorem TrivSqZeroExt.snd_inl {R : Type u} (M : Type v) [Zero M] (r : R) : TrivSqZeroExt.snd (TrivSqZeroExt.inl r) = 0

@[simp]

theorem TrivSqZeroExt.fst_comp_inl {R : Type u} (M : Type v) [Zero M] : TrivSqZeroExt.fst ∘ TrivSqZeroExt.inl = id

@[simp]

theorem TrivSqZeroExt.snd_comp_inl {R : Type u} (M : Type v) [Zero M] : TrivSqZeroExt.snd ∘ TrivSqZeroExt.inl = 0

@[simp]

theorem TrivSqZeroExt.fst_inr (R : Type u) {M : Type v} [Zero R] (m : M) : TrivSqZeroExt.fst (TrivSqZeroExt.inr m) = 0

@[simp]

theorem TrivSqZeroExt.snd_inr (R : Type u) {M : Type v} [Zero R] (m : M) : TrivSqZeroExt.snd (TrivSqZeroExt.inr m) = m

@[simp]

theorem TrivSqZeroExt.fst_comp_inr (R : Type u) {M : Type v} [Zero R] : TrivSqZeroExt.fst ∘ TrivSqZeroExt.inr = 0

@[simp]

theorem TrivSqZeroExt.snd_comp_inr (R : Type u) {M : Type v} [Zero R] : TrivSqZeroExt.snd ∘ TrivSqZeroExt.inr = id

theorem TrivSqZeroExt.inl_injective {R : Type u} {M : Type v} [Zero M] : Function.Injective TrivSqZeroExt.inl

theorem TrivSqZeroExt.inr_injective {R : Type u} {M : Type v} [Zero R] : Function.Injective TrivSqZeroExt.inr

Structures inherited from Prod

Additive operators and scalar multiplication operate elementwise.

instance TrivSqZeroExt.inhabited {R : Type u} {M : Type v} [Inhabited R] [Inhabited M] : Inhabited (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.inhabited = instInhabitedProd

instance TrivSqZeroExt.zero {R : Type u} {M : Type v} [Zero R] [Zero M] : Zero (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.zero = Prod.instZero

instance TrivSqZeroExt.add {R : Type u} {M : Type v} [Add R] [Add M] : Add (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.add = Prod.instAdd

instance TrivSqZeroExt.sub {R : Type u} {M : Type v} [Sub R] [Sub M] : Sub (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.sub = Prod.instSub

instance TrivSqZeroExt.neg {R : Type u} {M : Type v} [Neg R] [Neg M] : Neg (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.neg = Prod.instNeg

instance TrivSqZeroExt.addSemigroup {R : Type u} {M : Type v} [AddSemigroup R] [AddSemigroup M] : AddSemigroup (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addSemigroup = Prod.instAddSemigroup

instance TrivSqZeroExt.addZeroClass {R : Type u} {M : Type v} [AddZeroClass R] [AddZeroClass M] : AddZeroClass (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addZeroClass = Prod.instAddZeroClass

instance TrivSqZeroExt.addMonoid {R : Type u} {M : Type v} [AddMonoid R] [AddMonoid M] : AddMonoid (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addMonoid = Prod.instAddMonoid

instance TrivSqZeroExt.addGroup {R : Type u} {M : Type v} [AddGroup R] [AddGroup M] : AddGroup (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addGroup = Prod.instAddGroup

instance TrivSqZeroExt.addCommSemigroup {R : Type u} {M : Type v} [AddCommSemigroup R] [AddCommSemigroup M] : AddCommSemigroup (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addCommSemigroup = Prod.instAddCommSemigroup

instance TrivSqZeroExt.addCommMonoid {R : Type u} {M : Type v} [AddCommMonoid R] [AddCommMonoid M] : AddCommMonoid (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addCommMonoid = Prod.instAddCommMonoid

instance TrivSqZeroExt.addCommGroup {R : Type u} {M : Type v} [AddCommGroup R] [AddCommGroup M] : AddCommGroup (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addCommGroup = Prod.instAddCommGroup

instance TrivSqZeroExt.smul {S : Type u_2} {R : Type u} {M : Type v} [SMul S R] [SMul S M] : SMul S (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.smul = Prod.smul

instance TrivSqZeroExt.isScalarTower {T : Type u_1} {S : Type u_2} {R : Type u} {M : Type v} [SMul T R] [SMul T M] [SMul S R] [SMul S M] [SMul T S] [IsScalarTower T S R] [IsScalarTower T S M] : IsScalarTower T S (TrivSqZeroExt R M)

Equations

• (_ : IsScalarTower T S (TrivSqZeroExt R M)) = (_ : IsScalarTower T S (R × M))

instance TrivSqZeroExt.smulCommClass {T : Type u_1} {S : Type u_2} {R : Type u} {M : Type v} [SMul T R] [SMul T M] [SMul S R] [SMul S M] [SMulCommClass T S R] [SMulCommClass T S M] : SMulCommClass T S (TrivSqZeroExt R M)

Equations

• (_ : SMulCommClass T S (TrivSqZeroExt R M)) = (_ : SMulCommClass T S (R × M))

instance TrivSqZeroExt.isCentralScalar {S : Type u_2} {R : Type u} {M : Type v} [SMul S R] [SMul S M] [SMul Sᵐᵒᵖ R] [SMul Sᵐᵒᵖ M] [IsCentralScalar S R] [IsCentralScalar S M] : IsCentralScalar S (TrivSqZeroExt R M)

Equations

• (_ : IsCentralScalar S (TrivSqZeroExt R M)) = (_ : IsCentralScalar S (R × M))

instance TrivSqZeroExt.mulAction {S : Type u_2} {R : Type u} {M : Type v} [Monoid S] [MulAction S R] [MulAction S M] : MulAction S (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.mulAction = Prod.mulAction

instance TrivSqZeroExt.distribMulAction {S : Type u_2} {R : Type u} {M : Type v} [Monoid S] [AddMonoid R] [AddMonoid M] [DistribMulAction S R] [DistribMulAction S M] : DistribMulAction S (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.distribMulAction = Prod.distribMulAction

instance TrivSqZeroExt.module {S : Type u_2} {R : Type u} {M : Type v} [Semiring S] [AddCommMonoid R] [AddCommMonoid M] [Module S R] [Module S M] : Module S (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.module = Prod.instModule

@[simp]

theorem TrivSqZeroExt.fst_zero {R : Type u} {M : Type v} [Zero R] [Zero M] : TrivSqZeroExt.fst 0 = 0

@[simp]

theorem TrivSqZeroExt.snd_zero {R : Type u} {M : Type v} [Zero R] [Zero M] : TrivSqZeroExt.snd 0 = 0

@[simp]

theorem TrivSqZeroExt.fst_add {R : Type u} {M : Type v} [Add R] [Add M] (x₁ : TrivSqZeroExt R M) (x₂ : TrivSqZeroExt R M) : TrivSqZeroExt.fst (x₁ + x₂) = TrivSqZeroExt.fst x₁ + TrivSqZeroExt.fst x₂

@[simp]

theorem TrivSqZeroExt.snd_add {R : Type u} {M : Type v} [Add R] [Add M] (x₁ : TrivSqZeroExt R M) (x₂ : TrivSqZeroExt R M) : TrivSqZeroExt.snd (x₁ + x₂) = TrivSqZeroExt.snd x₁ + TrivSqZeroExt.snd x₂

@[simp]

theorem TrivSqZeroExt.fst_neg {R : Type u} {M : Type v} [Neg R] [Neg M] (x : TrivSqZeroExt R M) : TrivSqZeroExt.fst (-x) = -TrivSqZeroExt.fst x

@[simp]

theorem TrivSqZeroExt.snd_neg {R : Type u} {M : Type v} [Neg R] [Neg M] (x : TrivSqZeroExt R M) : TrivSqZeroExt.snd (-x) = -TrivSqZeroExt.snd x

@[simp]

theorem TrivSqZeroExt.fst_sub {R : Type u} {M : Type v} [Sub R] [Sub M] (x₁ : TrivSqZeroExt R M) (x₂ : TrivSqZeroExt R M) : TrivSqZeroExt.fst (x₁ - x₂) = TrivSqZeroExt.fst x₁ - TrivSqZeroExt.fst x₂

@[simp]

theorem TrivSqZeroExt.snd_sub {R : Type u} {M : Type v} [Sub R] [Sub M] (x₁ : TrivSqZeroExt R M) (x₂ : TrivSqZeroExt R M) : TrivSqZeroExt.snd (x₁ - x₂) = TrivSqZeroExt.snd x₁ - TrivSqZeroExt.snd x₂

@[simp]

theorem TrivSqZeroExt.fst_smul {S : Type u_2} {R : Type u} {M : Type v} [SMul S R] [SMul S M] (s : S) (x : TrivSqZeroExt R M) : TrivSqZeroExt.fst (s • x) = s • TrivSqZeroExt.fst x

@[simp]

theorem TrivSqZeroExt.snd_smul {S : Type u_2} {R : Type u} {M : Type v} [SMul S R] [SMul S M] (s : S) (x : TrivSqZeroExt R M) : TrivSqZeroExt.snd (s • x) = s • TrivSqZeroExt.snd x

theorem TrivSqZeroExt.fst_sum {R : Type u} {M : Type v} {ι : Type u_3} [AddCommMonoid R] [AddCommMonoid M] (s : Finset ι) (f : ι → TrivSqZeroExt R M) : TrivSqZeroExt.fst (Finset.sum s fun (i : ι) => f i) = Finset.sum s fun (i : ι) => TrivSqZeroExt.fst (f i)

theorem TrivSqZeroExt.snd_sum {R : Type u} {M : Type v} {ι : Type u_3} [AddCommMonoid R] [AddCommMonoid M] (s : Finset ι) (f : ι → TrivSqZeroExt R M) : TrivSqZeroExt.snd (Finset.sum s fun (i : ι) => f i) = Finset.sum s fun (i : ι) => TrivSqZeroExt.snd (f i)

@[simp]

theorem TrivSqZeroExt.inl_zero {R : Type u} (M : Type v) [Zero R] [Zero M] : TrivSqZeroExt.inl 0 = 0

@[simp]

theorem TrivSqZeroExt.inl_add {R : Type u} (M : Type v) [Add R] [AddZeroClass M] (r₁ : R) (r₂ : R) : TrivSqZeroExt.inl (r₁ + r₂) = TrivSqZeroExt.inl r₁ + TrivSqZeroExt.inl r₂

@[simp]

theorem TrivSqZeroExt.inl_neg {R : Type u} (M : Type v) [Neg R] [SubNegZeroMonoid M] (r : R) : TrivSqZeroExt.inl (-r) = -TrivSqZeroExt.inl r

@[simp]

theorem TrivSqZeroExt.inl_sub {R : Type u} (M : Type v) [Sub R] [SubNegZeroMonoid M] (r₁ : R) (r₂ : R) : TrivSqZeroExt.inl (r₁ - r₂) = TrivSqZeroExt.inl r₁ - TrivSqZeroExt.inl r₂

@[simp]

theorem TrivSqZeroExt.inl_smul {S : Type u_2} {R : Type u} (M : Type v) [Monoid S] [AddMonoid M] [SMul S R] [DistribMulAction S M] (s : S) (r : R) : TrivSqZeroExt.inl (s • r) = s • TrivSqZeroExt.inl r

theorem TrivSqZeroExt.inl_sum {R : Type u} (M : Type v) {ι : Type u_3} [AddCommMonoid R] [AddCommMonoid M] (s : Finset ι) (f : ι → R) : TrivSqZeroExt.inl (Finset.sum s fun (i : ι) => f i) = Finset.sum s fun (i : ι) => TrivSqZeroExt.inl (f i)

@[simp]

theorem TrivSqZeroExt.inr_zero (R : Type u) {M : Type v} [Zero R] [Zero M] : TrivSqZeroExt.inr 0 = 0

@[simp]

theorem TrivSqZeroExt.inr_add (R : Type u) {M : Type v} [AddZeroClass R] [AddZeroClass M] (m₁ : M) (m₂ : M) : TrivSqZeroExt.inr (m₁ + m₂) = TrivSqZeroExt.inr m₁ + TrivSqZeroExt.inr m₂

@[simp]

theorem TrivSqZeroExt.inr_neg (R : Type u) {M : Type v} [SubNegZeroMonoid R] [Neg M] (m : M) : TrivSqZeroExt.inr (-m) = -TrivSqZeroExt.inr m

@[simp]

theorem TrivSqZeroExt.inr_sub (R : Type u) {M : Type v} [SubNegZeroMonoid R] [Sub M] (m₁ : M) (m₂ : M) : TrivSqZeroExt.inr (m₁ - m₂) = TrivSqZeroExt.inr m₁ - TrivSqZeroExt.inr m₂

@[simp]

theorem TrivSqZeroExt.inr_smul {S : Type u_2} (R : Type u) {M : Type v} [Zero R] [Zero S] [SMulWithZero S R] [SMul S M] (r : S) (m : M) : TrivSqZeroExt.inr (r • m) = r • TrivSqZeroExt.inr m

theorem TrivSqZeroExt.inr_sum (R : Type u) {M : Type v} {ι : Type u_3} [AddCommMonoid R] [AddCommMonoid M] (s : Finset ι) (f : ι → M) : TrivSqZeroExt.inr (Finset.sum s fun (i : ι) => f i) = Finset.sum s fun (i : ι) => TrivSqZeroExt.inr (f i)

theorem TrivSqZeroExt.inl_fst_add_inr_snd_eq {R : Type u} {M : Type v} [AddZeroClass R] [AddZeroClass M] (x : TrivSqZeroExt R M) : TrivSqZeroExt.inl (TrivSqZeroExt.fst x) + TrivSqZeroExt.inr (TrivSqZeroExt.snd x) = x

theorem TrivSqZeroExt.ind {R : Type u_3} {M : Type u_4} [AddZeroClass R] [AddZeroClass M] {P : TrivSqZeroExt R M → Prop} (h : ∀ (r : R) (m : M), P (TrivSqZeroExt.inl r + TrivSqZeroExt.inr m)) (x : TrivSqZeroExt R M) : P x

To show a property hold on all TrivSqZeroExt R M it suffices to show it holds on terms of the form inl r + inr m.

This can be used as induction x using TrivSqZeroExt.ind.

theorem TrivSqZeroExt.linearMap_ext {S : Type u_2} {R : Type u} {M : Type v} {N : Type u_3} [Semiring S] [AddCommMonoid R] [AddCommMonoid M] [AddCommMonoid N] [Module S R] [Module S M] [Module S N] ⦃f : TrivSqZeroExt R M →ₗ[S] N⦄ ⦃g : TrivSqZeroExt R M →ₗ[S] N⦄ (hl : ∀ (r : R), f (TrivSqZeroExt.inl r) = g (TrivSqZeroExt.inl r)) (hr : ∀ (m : M), f (TrivSqZeroExt.inr m) = g (TrivSqZeroExt.inr m)) : f = g

This cannot be marked @[ext] as it ends up being used instead of LinearMap.prod_ext when working with R × M.

@[simp]

theorem TrivSqZeroExt.inrHom_apply (R : Type u) (M : Type v) [Semiring R] [AddCommMonoid M] [Module R M] (m : M) : (TrivSqZeroExt.inrHom R M) m = TrivSqZeroExt.inr m

def TrivSqZeroExt.inrHom (R : Type u) (M : Type v) [Semiring R] [AddCommMonoid M] [Module R M] : M →ₗ[R] TrivSqZeroExt R M

The canonical R-linear inclusion M → TrivSqZeroExt R M.

Equations

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

@[simp]

theorem TrivSqZeroExt.sndHom_apply (R : Type u) (M : Type v) [Semiring R] [AddCommMonoid M] [Module R M] (x : TrivSqZeroExt R M) : (TrivSqZeroExt.sndHom R M) x = TrivSqZeroExt.snd x

def TrivSqZeroExt.sndHom (R : Type u) (M : Type v) [Semiring R] [AddCommMonoid M] [Module R M] : TrivSqZeroExt R M →ₗ[R] M

The canonical R-linear projection TrivSqZeroExt R M → M.

Equations

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

Multiplicative structure

instance TrivSqZeroExt.one {R : Type u} {M : Type v} [One R] [Zero M] : One (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.one = { one := (1, 0) }

instance TrivSqZeroExt.mul {R : Type u} {M : Type v} [Mul R] [Add M] [SMul R M] [SMul Rᵐᵒᵖ M] : Mul (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.mul = { mul := fun (x y : TrivSqZeroExt R M) => (x.1 * y.1, x.1 • y.2 + MulOpposite.op y.1 • x.2) }

@[simp]

theorem TrivSqZeroExt.fst_one {R : Type u} {M : Type v} [One R] [Zero M] : TrivSqZeroExt.fst 1 = 1

@[simp]

theorem TrivSqZeroExt.snd_one {R : Type u} {M : Type v} [One R] [Zero M] : TrivSqZeroExt.snd 1 = 0

@[simp]

theorem TrivSqZeroExt.fst_mul {R : Type u} {M : Type v} [Mul R] [Add M] [SMul R M] [SMul Rᵐᵒᵖ M] (x₁ : TrivSqZeroExt R M) (x₂ : TrivSqZeroExt R M) : TrivSqZeroExt.fst (x₁ * x₂) = TrivSqZeroExt.fst x₁ * TrivSqZeroExt.fst x₂

@[simp]

theorem TrivSqZeroExt.snd_mul {R : Type u} {M : Type v} [Mul R] [Add M] [SMul R M] [SMul Rᵐᵒᵖ M] (x₁ : TrivSqZeroExt R M) (x₂ : TrivSqZeroExt R M) : TrivSqZeroExt.snd (x₁ * x₂) = TrivSqZeroExt.fst x₁ • TrivSqZeroExt.snd x₂ + MulOpposite.op (TrivSqZeroExt.fst x₂) • TrivSqZeroExt.snd x₁

@[simp]

theorem TrivSqZeroExt.inl_one {R : Type u} (M : Type v) [One R] [Zero M] : TrivSqZeroExt.inl 1 = 1

@[simp]

theorem TrivSqZeroExt.inl_mul {R : Type u} (M : Type v) [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] (r₁ : R) (r₂ : R) : TrivSqZeroExt.inl (r₁ * r₂) = TrivSqZeroExt.inl r₁ * TrivSqZeroExt.inl r₂

theorem TrivSqZeroExt.inl_mul_inl {R : Type u} (M : Type v) [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] (r₁ : R) (r₂ : R) : TrivSqZeroExt.inl r₁ * TrivSqZeroExt.inl r₂ = TrivSqZeroExt.inl (r₁ * r₂)

@[simp]

theorem TrivSqZeroExt.inr_mul_inr (R : Type u) {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] (m₁ : M) (m₂ : M) : TrivSqZeroExt.inr m₁ * TrivSqZeroExt.inr m₂ = 0

theorem TrivSqZeroExt.inl_mul_inr {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] (r : R) (m : M) : TrivSqZeroExt.inl r * TrivSqZeroExt.inr m = TrivSqZeroExt.inr (r • m)

theorem TrivSqZeroExt.inr_mul_inl {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] (r : R) (m : M) : TrivSqZeroExt.inr m * TrivSqZeroExt.inl r = TrivSqZeroExt.inr (MulOpposite.op r • m)

theorem TrivSqZeroExt.inl_mul_eq_smul {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] (r : R) (x : TrivSqZeroExt R M) : TrivSqZeroExt.inl r * x = r • x

theorem TrivSqZeroExt.mul_inl_eq_op_smul {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] (x : TrivSqZeroExt R M) (r : R) : x * TrivSqZeroExt.inl r = MulOpposite.op r • x

instance TrivSqZeroExt.mulOneClass {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] : MulOneClass (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.mulOneClass = let src := TrivSqZeroExt.one; let src_1 := TrivSqZeroExt.mul; MulOneClass.mk (_ : ∀ (x : TrivSqZeroExt R M), 1 * x = x) (_ : ∀ (x : TrivSqZeroExt R M), x * 1 = x)

instance TrivSqZeroExt.addMonoidWithOne {R : Type u} {M : Type v} [AddMonoidWithOne R] [AddMonoid M] : AddMonoidWithOne (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addMonoidWithOne = let src := TrivSqZeroExt.addMonoid; let src_1 := TrivSqZeroExt.one; AddMonoidWithOne.mk

@[simp]

theorem TrivSqZeroExt.fst_nat_cast {R : Type u} {M : Type v} [AddMonoidWithOne R] [AddMonoid M] (n : ℕ) : TrivSqZeroExt.fst ↑n = ↑n

@[simp]

theorem TrivSqZeroExt.snd_nat_cast {R : Type u} {M : Type v} [AddMonoidWithOne R] [AddMonoid M] (n : ℕ) : TrivSqZeroExt.snd ↑n = 0

@[simp]

theorem TrivSqZeroExt.inl_nat_cast {R : Type u} {M : Type v} [AddMonoidWithOne R] [AddMonoid M] (n : ℕ) : TrivSqZeroExt.inl ↑n = ↑n

instance TrivSqZeroExt.addGroupWithOne {R : Type u} {M : Type v} [AddGroupWithOne R] [AddGroup M] : AddGroupWithOne (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.addGroupWithOne = let src := TrivSqZeroExt.addGroup; let src_1 := TrivSqZeroExt.addMonoidWithOne; AddGroupWithOne.mk SubNegMonoid.zsmul (_ : ∀ (a : TrivSqZeroExt R M), -a + a = 0)

@[simp]

theorem TrivSqZeroExt.fst_int_cast {R : Type u} {M : Type v} [AddGroupWithOne R] [AddGroup M] (z : ℤ) : TrivSqZeroExt.fst ↑z = ↑z

@[simp]

theorem TrivSqZeroExt.snd_int_cast {R : Type u} {M : Type v} [AddGroupWithOne R] [AddGroup M] (z : ℤ) : TrivSqZeroExt.snd ↑z = 0

@[simp]

theorem TrivSqZeroExt.inl_int_cast {R : Type u} {M : Type v} [AddGroupWithOne R] [AddGroup M] (z : ℤ) : TrivSqZeroExt.inl ↑z = ↑z

instance TrivSqZeroExt.nonAssocSemiring {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] : NonAssocSemiring (TrivSqZeroExt R M)

Equations

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

instance TrivSqZeroExt.nonAssocRing {R : Type u} {M : Type v} [Ring R] [AddCommGroup M] [Module R M] [Module Rᵐᵒᵖ M] : NonAssocRing (TrivSqZeroExt R M)

Equations

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

instance TrivSqZeroExt.instPowTrivSqZeroExtNat {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] : Pow (TrivSqZeroExt R M) ℕ

In the general non-commutative case, the power operator is

$$\begin{align} (r + m)^n &= r^n + r^{n-1}m + r^{n-2}mr + \cdots + rmr^{n-2} + mr^{n-1} \ & =r^n + \sum_{i = 0}^{n - 1} r^{(n - 1) - i} m r^{i} \end{align}$$

In the commutative case this becomes the simpler $(r + m)^n = r^n + nr^{n-1}m$.

Equations

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

@[simp]

theorem TrivSqZeroExt.fst_pow {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] (x : TrivSqZeroExt R M) (n : ℕ) : TrivSqZeroExt.fst (x ^ n) = TrivSqZeroExt.fst x ^ n

theorem TrivSqZeroExt.snd_pow_eq_sum {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] (x : TrivSqZeroExt R M) (n : ℕ) : TrivSqZeroExt.snd (x ^ n) = List.sum (List.map (fun (i : ℕ) => TrivSqZeroExt.fst x ^ (Nat.pred n - i) • MulOpposite.op (TrivSqZeroExt.fst x ^ i) • TrivSqZeroExt.snd x) (List.range n))

theorem TrivSqZeroExt.snd_pow_of_smul_comm {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] (x : TrivSqZeroExt R M) (n : ℕ) (h : MulOpposite.op (TrivSqZeroExt.fst x) • TrivSqZeroExt.snd x = TrivSqZeroExt.fst x • TrivSqZeroExt.snd x) : TrivSqZeroExt.snd (x ^ n) = n • TrivSqZeroExt.fst x ^ Nat.pred n • TrivSqZeroExt.snd x

@[simp]

theorem TrivSqZeroExt.snd_pow {R : Type u} {M : Type v} [CommMonoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] [IsCentralScalar R M] (x : TrivSqZeroExt R M) (n : ℕ) : TrivSqZeroExt.snd (x ^ n) = n • TrivSqZeroExt.fst x ^ Nat.pred n • TrivSqZeroExt.snd x

@[simp]

theorem TrivSqZeroExt.inl_pow {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] (r : R) (n : ℕ) : TrivSqZeroExt.inl r ^ n = TrivSqZeroExt.inl (r ^ n)

instance TrivSqZeroExt.monoid {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] : Monoid (TrivSqZeroExt R M)

Equations

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

theorem TrivSqZeroExt.fst_list_prod {R : Type u} {M : Type v} [Monoid R] [AddMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] (l : List (TrivSqZeroExt R M)) : TrivSqZeroExt.fst (List.prod l) = List.prod (List.map TrivSqZeroExt.fst l)

instance TrivSqZeroExt.semiring {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] : Semiring (TrivSqZeroExt R M)

Equations

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

theorem TrivSqZeroExt.snd_list_prod {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] (l : List (TrivSqZeroExt R M)) : TrivSqZeroExt.snd (List.prod l) = List.sum (List.map (fun (x : ℕ × TrivSqZeroExt R M) => List.prod (List.take x.1 (List.map TrivSqZeroExt.fst l)) • MulOpposite.op (List.prod (List.drop (Nat.succ x.1) (List.map TrivSqZeroExt.fst l))) • TrivSqZeroExt.snd x.2) (List.enum l))

The second element of a product $\prod_{i=0}^n (r_i + m_i)$ is a sum of terms of the form $r_0\cdots r_{i-1}m_ir_{i+1}\cdots r_n$.

instance TrivSqZeroExt.ring {R : Type u} {M : Type v} [Ring R] [AddCommGroup M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] : Ring (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.ring = let src := TrivSqZeroExt.semiring; let src_1 := TrivSqZeroExt.nonAssocRing; Ring.mk SubNegMonoid.zsmul (_ : ∀ (a : TrivSqZeroExt R M), -a + a = 0)

instance TrivSqZeroExt.commMonoid {R : Type u} {M : Type v} [CommMonoid R] [AddCommMonoid M] [DistribMulAction R M] [DistribMulAction Rᵐᵒᵖ M] [IsCentralScalar R M] : CommMonoid (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.commMonoid = let src := TrivSqZeroExt.monoid; CommMonoid.mk (_ : ∀ (x₁ x₂ : TrivSqZeroExt R M), x₁ * x₂ = x₂ * x₁)

instance TrivSqZeroExt.commSemiring {R : Type u} {M : Type v} [CommSemiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] [IsCentralScalar R M] : CommSemiring (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.commSemiring = let src := TrivSqZeroExt.commMonoid; let src_1 := TrivSqZeroExt.nonAssocSemiring; CommSemiring.mk (_ : ∀ (a b : TrivSqZeroExt R M), a * b = b * a)

instance TrivSqZeroExt.commRing {R : Type u} {M : Type v} [CommRing R] [AddCommGroup M] [Module R M] [Module Rᵐᵒᵖ M] [IsCentralScalar R M] : CommRing (TrivSqZeroExt R M)

Equations

• TrivSqZeroExt.commRing = let src := TrivSqZeroExt.nonAssocRing; let src_1 := TrivSqZeroExt.commSemiring; CommRing.mk (_ : ∀ (a b : TrivSqZeroExt R M), a * b = b * a)

@[simp]

theorem TrivSqZeroExt.inlHom_apply (R : Type u) (M : Type v) [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] (r : R) : (TrivSqZeroExt.inlHom R M) r = TrivSqZeroExt.inl r

def TrivSqZeroExt.inlHom (R : Type u) (M : Type v) [Semiring R] [AddCommMonoid M] [Module R M] [Module Rᵐᵒᵖ M] : R →+* TrivSqZeroExt R M

The canonical inclusion of rings R → TrivSqZeroExt R M.

Equations

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

instance TrivSqZeroExt.algebra' (S : Type u_1) (R : Type u) (M : Type v) [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] : Algebra S (TrivSqZeroExt R M)

Equations

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

instance TrivSqZeroExt.instAlgebraTrivSqZeroExtSemiringToSemiringOp_rightToSMulToZeroToAddMonoidToSMulZeroClassToZeroToMonoidWithZeroToSMulWithZeroToMulActionWithZeroToZeroToCommMonoidWithZeroMulOppositeZeroMonoidWithZeroSemiringSmulCommClass_selfToCommMonoidToMulAction (R' : Type u) (M : Type v) [CommSemiring R'] [AddCommMonoid M] [Module R' M] [Module R'ᵐᵒᵖ M] [IsCentralScalar R' M] : Algebra R' (TrivSqZeroExt R' M)

Equations

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

theorem TrivSqZeroExt.algebraMap_eq_inl (R' : Type u) (M : Type v) [CommSemiring R'] [AddCommMonoid M] [Module R' M] [Module R'ᵐᵒᵖ M] [IsCentralScalar R' M] : ⇑(algebraMap R' (TrivSqZeroExt R' M)) = TrivSqZeroExt.inl

theorem TrivSqZeroExt.algebraMap_eq_inlHom (R' : Type u) (M : Type v) [CommSemiring R'] [AddCommMonoid M] [Module R' M] [Module R'ᵐᵒᵖ M] [IsCentralScalar R' M] : algebraMap R' (TrivSqZeroExt R' M) = TrivSqZeroExt.inlHom R' M

theorem TrivSqZeroExt.algebraMap_eq_inl' (S : Type u_1) (R : Type u) (M : Type v) [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] (s : S) : (algebraMap S (TrivSqZeroExt R M)) s = TrivSqZeroExt.inl ((algebraMap S R) s)

@[simp]

theorem TrivSqZeroExt.fstHom_apply (S : Type u_1) (R : Type u) (M : Type v) [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] (x : TrivSqZeroExt R M) : (TrivSqZeroExt.fstHom S R M) x = TrivSqZeroExt.fst x

def TrivSqZeroExt.fstHom (S : Type u_1) (R : Type u) (M : Type v) [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] : TrivSqZeroExt R M →ₐ[S] R

The canonical S-algebra projection TrivSqZeroExt R M → R.

Equations

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

@[simp]

theorem TrivSqZeroExt.inlAlgHom_apply (S : Type u_1) (R : Type u) (M : Type v) [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] (r : R) : (TrivSqZeroExt.inlAlgHom S R M) r = TrivSqZeroExt.inl r

def TrivSqZeroExt.inlAlgHom (S : Type u_1) (R : Type u) (M : Type v) [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] : R →ₐ[S] TrivSqZeroExt R M

The canonical S-algebra inclusion R → TrivSqZeroExt R M.

Equations

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

theorem TrivSqZeroExt.algHom_ext {R' : Type u} {M : Type v} [CommSemiring R'] [AddCommMonoid M] [Module R' M] [Module R'ᵐᵒᵖ M] [IsCentralScalar R' M] {A : Type u_2} [Semiring A] [Algebra R' A] ⦃f : TrivSqZeroExt R' M →ₐ[R'] A⦄ ⦃g : TrivSqZeroExt R' M →ₐ[R'] A⦄ (h : ∀ (m : M), f (TrivSqZeroExt.inr m) = g (TrivSqZeroExt.inr m)) : f = g

theorem TrivSqZeroExt.algHom_ext' {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] ⦃f : TrivSqZeroExt R M →ₐ[S] A⦄ ⦃g : TrivSqZeroExt R M →ₐ[S] A⦄ (hinl : AlgHom.comp f (TrivSqZeroExt.inlAlgHom S R M) = AlgHom.comp g (TrivSqZeroExt.inlAlgHom S R M)) (hinr : AlgHom.toLinearMap f ∘ₗ ↑S (TrivSqZeroExt.inrHom R M) = AlgHom.toLinearMap g ∘ₗ ↑S (TrivSqZeroExt.inrHom R M)) : f = g

def TrivSqZeroExt.lift {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] (f : R →ₐ[S] A) (g : M →ₗ[S] A) (hg : ∀ (x y : M), g x * g y = 0) (hfg : ∀ (r : R) (x : M), g (r • x) = f r * g x) (hgf : ∀ (r : R) (x : M), g (MulOpposite.op r • x) = g x * f r) : TrivSqZeroExt R M →ₐ[S] A

Assemble an algebra morphism TrivSqZeroExt R M →ₐ[S] A from separate morphisms on R and M.

Namely, we require that for an algebra morphism f : R →ₐ[S] A and a linear map g : M →ₗ[S] A, we have:

• g x * g y = 0: the elements of M continue to square to zero.
• g (r • x) = f r * g x and g (op r • x) = g x * f r: scalar multiplication on the left and right is sent to left- and right- multiplication by the image under f.

See TrivSqZeroExt.liftEquiv for this as an equiv; namely that any such algebra morphism can be factored in this way.

When R is commutative, this can be invoked with f = Algebra.ofId R A, which satisfies hfg and hgf. This version is captured as an equiv by TrivSqZeroExt.liftEquivOfComm.

Equations

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

@[simp]

theorem TrivSqZeroExt.lift_apply_inl {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] (f : R →ₐ[S] A) (g : M →ₗ[S] A) (hg : ∀ (x y : M), g x * g y = 0) (hfg : ∀ (r : R) (x : M), g (r • x) = f r * g x) (hgf : ∀ (r : R) (x : M), g (MulOpposite.op r • x) = g x * f r) (r : R) : (TrivSqZeroExt.lift f g hg hfg hgf) (TrivSqZeroExt.inl r) = f r

@[simp]

theorem TrivSqZeroExt.lift_apply_inr {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] (f : R →ₐ[S] A) (g : M →ₗ[S] A) (hg : ∀ (x y : M), g x * g y = 0) (hfg : ∀ (r : R) (x : M), g (r • x) = f r * g x) (hgf : ∀ (r : R) (x : M), g (MulOpposite.op r • x) = g x * f r) (m : M) : (TrivSqZeroExt.lift f g hg hfg hgf) (TrivSqZeroExt.inr m) = g m

@[simp]

theorem TrivSqZeroExt.lift_comp_inlHom {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] (f : R →ₐ[S] A) (g : M →ₗ[S] A) (hg : ∀ (x y : M), g x * g y = 0) (hfg : ∀ (r : R) (x : M), g (r • x) = f r * g x) (hgf : ∀ (r : R) (x : M), g (MulOpposite.op r • x) = g x * f r) : AlgHom.comp (TrivSqZeroExt.lift f g hg hfg hgf) (TrivSqZeroExt.inlAlgHom S R M) = f

@[simp]

theorem TrivSqZeroExt.lift_comp_inrHom {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] (f : R →ₐ[S] A) (g : M →ₗ[S] A) (hg : ∀ (x y : M), g x * g y = 0) (hfg : ∀ (r : R) (x : M), g (r • x) = f r * g x) (hgf : ∀ (r : R) (x : M), g (MulOpposite.op r • x) = g x * f r) : AlgHom.toLinearMap (TrivSqZeroExt.lift f g hg hfg hgf) ∘ₗ ↑S (TrivSqZeroExt.inrHom R M) = g

@[simp]

theorem TrivSqZeroExt.lift_inlAlgHom_inrHom {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] : TrivSqZeroExt.lift (TrivSqZeroExt.inlAlgHom S R M) (↑S (TrivSqZeroExt.inrHom R M)) (_ : ∀ (m₁ m₂ : M), TrivSqZeroExt.inr m₁ * TrivSqZeroExt.inr m₂ = 0) (_ : ∀ (x : R) (x_1 : M), TrivSqZeroExt.inr (x • x_1) = TrivSqZeroExt.inl x * TrivSqZeroExt.inr x_1) (_ : ∀ (x : R) (x_1 : M), TrivSqZeroExt.inr (MulOpposite.op x • x_1) = TrivSqZeroExt.inr x_1 * TrivSqZeroExt.inl x) = AlgHom.id S (TrivSqZeroExt R M)

When applied to inr and inl themselves, lift is the identity.

@[simp]

theorem TrivSqZeroExt.liftEquiv_apply_apply {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] (fg : { fg : (R →ₐ[S] A) × (M →ₗ[S] A) // (∀ (x y : M), fg.2 x * fg.2 y = 0) ∧ (∀ (r : R) (x : M), fg.2 (r • x) = fg.1 r * fg.2 x) ∧ ∀ (r : R) (x : M), fg.2 (MulOpposite.op r • x) = fg.2 x * fg.1 r }) (a : TrivSqZeroExt R M) : (TrivSqZeroExt.liftEquiv fg) a = (↑fg).1 (TrivSqZeroExt.fst a) + (↑fg).2 (TrivSqZeroExt.snd a)

@[simp]

theorem TrivSqZeroExt.liftEquiv_symm_apply_coe {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] (F : TrivSqZeroExt R M →ₐ[S] A) : ↑(TrivSqZeroExt.liftEquiv.symm F) = (AlgHom.comp F (TrivSqZeroExt.inlAlgHom S R M), LinearMap.comp (AlgHom.toLinearMap F) (↑S (TrivSqZeroExt.inrHom R M)))

def TrivSqZeroExt.liftEquiv {S : Type u_1} {R : Type u} {M : Type v} [CommSemiring S] [Semiring R] [AddCommMonoid M] [Algebra S R] [Module S M] [Module R M] [Module Rᵐᵒᵖ M] [SMulCommClass R Rᵐᵒᵖ M] [IsScalarTower S R M] [IsScalarTower S Rᵐᵒᵖ M] {A : Type u_2} [Semiring A] [Algebra S A] : { fg : (R →ₐ[S] A) × (M →ₗ[S] A) // (∀ (x y : M), fg.2 x * fg.2 y = 0) ∧ (∀ (r : R) (x : M), fg.2 (r • x) = fg.1 r * fg.2 x) ∧ ∀ (r : R) (x : M), fg.2 (MulOpposite.op r • x) = fg.2 x * fg.1 r } ≃ (TrivSqZeroExt R M →ₐ[S] A)

A universal property of the trivial square-zero extension, providing a unique TrivSqZeroExt R M →ₐ[R] A for every pair of maps f : R →ₐ[S] A and g : M →ₗ[S] A, where the range of g has no non-zero products, and scaling the input to g on the left or right amounts to a corresponding multiplication by f in the output.

This isomorphism is named to match the very similar Complex.lift.

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def TrivSqZeroExt.liftEquivOfComm {R' : Type u} {M : Type v} [CommSemiring R'] [AddCommMonoid M] [Module R' M] [Module R'ᵐᵒᵖ M] [IsCentralScalar R' M] {A : Type u_2} [Semiring A] [Algebra R' A] : { f : M →ₗ[R'] A // ∀ (x y : M), f x * f y = 0 } ≃ (TrivSqZeroExt R' M →ₐ[R'] A)

A simplified version of TrivSqZeroExt.liftEquiv for the commutative case.

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