Equivariant homomorphisms #
Main definitions #
- MulActionHom φ X Y, the type of equivariant functions from- Xto- Y, where- φ : M → Nis a map,- Macting on the type- Xand- Nacting on the type of- Y.- AddActionHom φ X Yis its additive version.
- DistribMulActionHom φ A B, the type of equivariant additive monoid homomorphisms from- Ato- B, where- φ : M → Nis a morphism of monoids,- Macting on the additive monoid- Aand- Nacting on the additive monoid of- B
- SMulSemiringHom φ R S, the type of equivariant ring homomorphisms from- Rto- S, where- φ : M → Nis a morphism of monoids,- Macting on the ring- Rand- Nacting on the ring- S.
The above types have corresponding classes:
- MulActionHomClass F φ X Ystates that- Fis a type of bundled- X → Yhoms which are- φ-equivariant;- AddActionHomClass F φ X Yis its additive version.
- DistribMulActionHomClass F φ A Bstates that- Fis a type of bundled- A → Bhoms preserving the additive monoid structure and- φ-equivariant
- SMulSemiringHomClass F φ R Sstates that- Fis a type of bundled- R → Shoms preserving the ring structure and- φ-equivariant
Notation #
We introduce the following notation to code equivariant maps
(the subscript index ₑ is for equivariant) :
- X →ₑ[φ] Yis- MulActionHom φ X Yand- AddActionHom φ X Y
- A →ₑ+[φ] Bis- DistribMulActionHom φ A B.
- R →ₑ+*[φ] Sis- MulSemiringActionHom φ R S.
When M = N and φ = MonoidHom.id M, we provide the backward compatible notation :
- X →[M] Yis- MulActionHom (@id M) X Yand- AddActionHom (@id M) X Y
- A →+[M] Bis- DistribMulActionHom (MonoidHom.id M) A B
- R →+*[M] Sis- MulSemiringActionHom (MonoidHom.id M) R S
The notation for MulActionHom and AddActionHom is the same, because it is unlikely
that it could lead to confusion — unless one needs types M and X with simultaneous
instances of Mul M, Add M, SMul M X and VAdd M X…
Equivariant functions :
When φ : M → N is a function, and types X and Y are endowed with additive actions
of M and N, a function f : X → Y is φ-equivariant if f (m +ᵥ x) = (φ m) +ᵥ (f x).
- toFun : X → YThe underlying function. 
- The proposition that the function commutes with the additive actions. 
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Equivariant functions :
When φ : M → N is a function, and types X and Y are endowed with actions of M and N,
a function f : X → Y is φ-equivariant if f (m • x) = (φ m) • (f x).
- toFun : X → YThe underlying function. 
- The proposition that the function commutes with the actions. 
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φ-equivariant functions X → Y,
where φ : M → N, where M and N act on X and Y respectively.
Equations
- One or more equations did not get rendered due to their size.
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M-equivariant functions X → Y with respect to the action of M.
This is the same as X →ₑ[@id M] Y.
Equations
- One or more equations did not get rendered due to their size.
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φ-equivariant functions X → Y,
where φ : M → N, where M and N act additively on X and Y respectively
We use the same notation as for multiplicative actions, as conflicts are unlikely.
Equations
- One or more equations did not get rendered due to their size.
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M-equivariant functions X → Y with respect to the additive action of M.
This is the same as X →ₑ[@id M] Y.
We use the same notation as for multiplicative actions, as conflicts are unlikely.
Equations
- One or more equations did not get rendered due to their size.
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AddActionSemiHomClass F φ X Y states that
F is a type of morphisms which are φ-equivariant.
You should extend this class when you extend AddActionHom.
- The proposition that the function preserves the action. 
Instances
MulActionSemiHomClass F φ X Y states that
F is a type of morphisms which are φ-equivariant.
You should extend this class when you extend MulActionHom.
- The proposition that the function preserves the action. 
Instances
MulActionHomClass F M X Y states that F is a type of
morphisms which are equivariant with respect to actions of M
This is an abbreviation of MulActionSemiHomClass.
Equations
- MulActionHomClass F M X Y = MulActionSemiHomClass F id X Y
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MulActionHomClass F M X Y states that F is a type of
morphisms which are equivariant with respect to actions of M
This is an abbreviation of MulActionSemiHomClass.
Equations
- AddActionHomClass F M X Y = AddActionSemiHomClass F id X Y
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Turn an element of a type F satisfying MulActionSemiHomClass F φ X Y
into an actual MulActionHom.
This is declared as the default coercion from F to MulActionSemiHom φ X Y.
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Turn an element of a type F satisfying AddActionSemiHomClass F φ X Y
into an actual AddActionHom.
This is declared as the default coercion from F to AddActionSemiHom φ X Y.
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Any type satisfying MulActionSemiHomClass can be cast into MulActionHom via
MulActionHomSemiClass.toMulActionHom.
If Y/X/M forms a scalar tower, any map X → Y preserving X-action also preserves M-action.
Two equal maps on scalars give rise to an equivariant map for identity
Equations
- MulActionHom.ofEq h f = { toFun := f.toFun, map_smul' := ⋯ }
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Two equal maps on scalars give rise to an equivariant map for identity
Equations
- AddActionHom.ofEq h f = { toFun := f.toFun, map_vadd' := ⋯ }
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The inverse of a bijective equivariant map is equivariant.
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The inverse of a bijective equivariant map is equivariant.
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The inverse of a bijective equivariant map is equivariant.
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The inverse of a bijective equivariant map is equivariant.
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If actions of M and N on α commute,
then for c : M, (c • · : α → α) is an N-action homomorphism.
Equations
- SMulCommClass.toMulActionHom N α c = { toFun := fun (x : α) => c • x, map_smul' := ⋯ }
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If additive actions of M and N on α commute,
then for c : M, (c • · : α → α) is an N-additive action homomorphism.
Equations
- VAddCommClass.toAddActionHom N α c = { toFun := fun (x : α) => c +ᵥ x, map_vadd' := ⋯ }
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Evaluation at a point as a MulActionHom.
Equations
- Pi.evalMulActionHom i = { toFun := Function.eval i, map_smul' := ⋯ }
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Evaluation at a point as an AddActionHom.
Equations
- Pi.evalAddActionHom i = { toFun := Function.eval i, map_vadd' := ⋯ }
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Equations
- MulActionHom.instAddZeroClass = { toZero := MulActionHom.instZero, add := fun (f g : X →ₑ[σ] Y) => { toFun := ⇑f + ⇑g, map_smul' := ⋯ }, zero_add := ⋯, add_zero := ⋯ }
Equations
- MulActionHom.instAddCommMonoid = { toAddMonoid := MulActionHom.instAddMonoid, add_comm := ⋯ }
Equations
- MulActionHom.instMulActionOfSMulCommClass = { toSMul := MulActionHom.instSMulOfSMulCommClass, one_smul := ⋯, mul_smul := ⋯ }
Equations
- AddActionHom.instAddActionOfVAddCommClass = { toVAdd := AddActionHom.instVAddOfVAddCommClass, zero_vadd := ⋯, add_vadd := ⋯ }
Equations
- MulActionHom.instDistribSMulOfSMulCommClass = { toSMul := MulActionHom.instSMulOfSMulCommClass, smul_zero := ⋯, smul_add := ⋯ }
Equations
- MulActionHom.instDistribMulActionOfSMulCommClass = { toMulAction := inferInstanceAs (MulAction R (X →ₑ[σ] Y)), smul_zero := ⋯, smul_add := ⋯ }
Equations
- MulActionHom.instModuleOfSMulCommClass = { toDistribMulAction := MulActionHom.instDistribMulActionOfSMulCommClass, add_smul := ⋯, zero_smul := ⋯ }
Equations
- MulActionHom.instAddCommGroup = { toAddGroup := MulActionHom.instAddGroup, add_comm := ⋯ }
Equations
- MulActionHom.instCommMonoid = { toMonoid := MulActionHom.instMonoid, mul_comm := ⋯ }
Equations
- MulActionHom.instCommSemiring = { toSemiring := MulActionHom.instSemiring, mul_comm := ⋯ }
Equations
- MulActionHom.instCommRing = { toRing := MulActionHom.instRing, mul_comm := ⋯ }
Equivariant additive monoid homomorphisms.
- toFun : A → B
Instances For
Equivariant additive monoid homomorphisms.
Equations
- One or more equations did not get rendered due to their size.
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Equivariant additive monoid homomorphisms.
Equations
- One or more equations did not get rendered due to their size.
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DistribMulActionSemiHomClass F φ A B states that F is a type of morphisms
preserving the additive monoid structure and equivariant with respect to φ.
You should extend this class when you extend DistribMulActionSemiHom.
Instances
DistribMulActionHomClass F M A B states that F is a type of morphisms preserving
the additive monoid structure and equivariant with respect to the action of M.
It is an abbreviation to DistribMulActionHomClass F (MonoidHom.id M) A B
You should extend this class when you extend DistribMulActionHom.
Equations
- DistribMulActionHomClass F M A B = DistribMulActionSemiHomClass F (⇑(MonoidHom.id M)) A B
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Turn an element of a type F satisfying MulActionHomClass F M X Y into an actual
MulActionHom. This is declared as the default coercion from F to MulActionHom M X Y.
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Any type satisfying MulActionHomClass can be cast into MulActionHom
via MulActionHomClass.toMulActionHom.
If DistribMulAction of M and N on A commute,
then for each c : M, (c • ·) is an N-action additive homomorphism.
Equations
- SMulCommClass.toDistribMulActionHom N A c = { toFun := fun (x : A) => c • x, map_smul' := ⋯, map_zero' := ⋯, map_add' := ⋯ }
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The identity map as an equivariant additive monoid homomorphism.
Equations
- DistribMulActionHom.id M = { toMulActionHom := MulActionHom.id M, map_zero' := ⋯, map_add' := ⋯ }
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Equations
Equations
- DistribMulActionHom.instInhabited = { default := 0 }
Composition of two equivariant additive monoid homomorphisms.
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The inverse of a bijective DistribMulActionHom is a DistribMulActionHom.
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Equivariant ring homomorphisms.
- toFun : R → S
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Equivariant ring homomorphisms.
Equations
- One or more equations did not get rendered due to their size.
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Equivariant ring homomorphisms.
Equations
- One or more equations did not get rendered due to their size.
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MulSemiringActionHomClass F φ R S states that F is a type of morphisms preserving
the ring structure and equivariant with respect to φ.
You should extend this class when you extend MulSemiringActionHom.
Instances
MulSemiringActionHomClass F M R S states that F is a type of morphisms preserving
the ring structure and equivariant with respect to a DistribMulActionof M on R and S .
Equations
- MulSemiringActionHomClass F R S = MulSemiringActionSemiHomClass F (⇑(MonoidHom.id M)) R S
Instances For
Turn an element of a type F satisfying MulSemiringActionHomClass F M R S into an actual
MulSemiringActionHom. This is declared as the default coercion from F to
MulSemiringActionHom M X Y.
Equations
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Any type satisfying MulSemiringActionHomClass can be cast into MulSemiringActionHom via
MulSemiringActionHomClass.toMulSemiringActionHom.
The identity map as an equivariant ring homomorphism.
Equations
- MulSemiringActionHom.id M = { toDistribMulActionHom := DistribMulActionHom.id M, map_one' := ⋯, map_mul' := ⋯ }
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Composition of two equivariant additive ring homomorphisms.
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The inverse of a bijective MulSemiringActionHom is a MulSemiringActionHom.
Equations
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The inverse of a bijective MulSemiringActionHom is a MulSemiringActionHom.