Equivariant homomorphisms #
Main definitions #
MulActionHom φ X Y, the type of equivariant functions fromXtoY, whereφ : M → Nis a map,Macting on the typeXandNacting on the type ofY.AddActionHom φ X Yis its additive version.DistribMulActionHom φ A B, the type of equivariant additive monoid homomorphisms fromAtoB, whereφ : M → Nis a morphism of monoids,Macting on the additive monoidAandNacting on the additive monoid ofBSMulSemiringHom φ R S, the type of equivariant ring homomorphisms fromRtoS, whereφ : M → Nis a morphism of monoids,Macting on the ringRandNacting on the ringS.
The above types have corresponding classes:
MulActionHomClass F φ X Ystates thatFis a type of bundledX → Yhoms which areφ-equivariant;AddActionHomClass F φ X Yis its additive version.DistribMulActionHomClass F φ A Bstates thatFis a type of bundledA → Bhoms preserving the additive monoid structure andφ-equivariantSMulSemiringHomClass F φ R Sstates thatFis a type of bundledR → Shoms preserving the ring structure andφ-equivariant
Notation #
We introduce the following notation to code equivariant maps
(the subscript index ₑ is for equivariant) :
X →ₑ[φ] YisMulActionHom φ X YandAddActionHom φ X YA →ₑ+[φ] BisDistribMulActionHom φ A B.R →ₑ+*[φ] SisMulSemiringActionHom φ R S.
When M = N and φ = MonoidHom.id M, we provide the backward compatible notation :
X →[M] YisMulActionHom (@id M) X YandAddActionHom (@id M) X YA →+[M] BisDistribMulActionHom (MonoidHom.id M) A BR →+*[M] SisMulSemiringActionHom (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 → Y
The 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 → Y
The 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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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If Y/X/M forms a scalar tower, any map X → Y preserving X-action also preserves M-action.
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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Evaluation at a point as a MulActionHom.
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Evaluation at a point as an AddActionHom.
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Equivariant additive monoid homomorphisms.
- toFun : A → B
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Equivariant additive monoid homomorphisms.
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Equivariant additive monoid homomorphisms.
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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.
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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.
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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.
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If DistribMulAction of M and N on A commute,
then for each c : M, (c • ·) is an N-action additive homomorphism.
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The identity map as an equivariant additive monoid homomorphism.
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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.
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Equivariant ring homomorphisms.
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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.
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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 .
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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.
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Any type satisfying MulSemiringActionHomClass can be cast into MulSemiringActionHom via
MulSemiringActionHomClass.toMulSemiringActionHom.
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The identity map as an equivariant ring homomorphism.
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Composition of two equivariant additive ring homomorphisms.
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The inverse of a bijective MulSemiringActionHom is a MulSemiringActionHom.
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The inverse of a bijective MulSemiringActionHom is a MulSemiringActionHom.