Physlib.Relativity.Tensors.Color.Lift
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Isomorphism from a morphism in a discrete category
#homToIsoIn the discrete category associated with a type , a morphism exists if and only if . This function takes such a morphism and returns the canonical isomorphism induced by this equality.
Tensor product representation of an `OverColor` object
#toRepGiven a functor , which assigns a representation of a group over a field to each "color" in , and an object (which consists of an indexing set and a mapping ), the representation `toRep F f` is defined as the tensor product of representations corresponding to the colors in . Specifically, the underlying vector space is the tensor product , where is the representation space of . For any group element , its action on the tensor product is given by the tensor product of the individual actions: where is the linear map corresponding to in the representation .
Let be a functor that assigns a representation of a group over a field to each "color" in . For any object (consisting of an indexing set and a mapping ) and any group element , the linear map representing the action of on the tensor product representation is equal to the tensor product of the linear maps representing the action of on each constituent representation . Mathematically, this is expressed as: where the right-hand side denotes the linear map on the tensor product space induced by the collection of individual group actions.
Group action on elementary tensors in the representation
#toRep_ρ_tprodLet be a functor that assigns a representation of a group over a field to each color in . For an object , which consists of an indexing set and a mapping , let be the representation defined by the tensor product of the representations for . For any group element and any collection of vectors where belongs to the representation space of , the action of on the elementary tensor is equal to the elementary tensor of the individual actions:
The group action on the representation of the monoidal unit is the identity map
#toRep_ρ_emptyLet be a functor that assigns a representation of a group over a field to each color in . Let denote the monoidal unit object in the category (which corresponds to an empty indexing set). For any group element , the linear map representing the action of on the resulting representation is the identity map: This reflects the fact that the representation associated with the monoidal unit (an empty tensor product) is the trivial representation.
Let be a functor that assigns a representation of a group over a field to each color in . Consider a mapping , which defines an object in the category indexed by the empty set . For any group element , the linear map representing the action of on the associated tensor product representation is the identity map: This result confirms that the representation formed from an empty collection of indices (using the specific index set ) is the trivial representation.
The underlying vector space of is the tensor product
#toRep_V_carrierLet be a collection of colors and be a functor that assigns a representation of a group over a field to each color. For any object in the category , which consists of an indexing set (referred to as ) and a mapping , the underlying vector space of the representation is the tensor product over of the vector spaces of the representations assigned to each color :
Linear equivalence from equality
#linearIsoOfEqLet be a set of colors and be a functor that assigns a representation of a group over a field to each color. Given two colors and a proof of their equality, this definition provides the -linear equivalence between the underlying vector spaces of the representations and , denoted as . This isomorphism is induced by the functorial image of the unique isomorphism in the discrete category corresponding to the equality .
The linear isomorphism commutes with the representation action
#linearIsoOfEq_comm_ρLet be a set of colors and be a functor that assigns a representation of a group over a field to each color. Given two colors and a proof that they are equal, let be the -linear equivalence between the underlying vector spaces of the representations induced by the equality. For any group element and any vector in the representation , applying the isomorphism commutes with the representation action :
Linear equivalence induced by a morphism
#linearIsoOfHomLet be a field, be a group, and be a functor mapping each "color" to a representation of . Given two objects (representing collections of colors indexed by sets and respectively) and a morphism , this definition provides a -linear equivalence between the underlying vector spaces of the associated tensor product representations: The isomorphism is constructed by reindexing the factors of the tensor product using the bijection and applying the linear isomorphisms induced by the identity of colors for each index.
Action of the induced isomorphism on elementary tensor products
#linearIsoOfHom_tprodLet be a field, a group, and a set of colors. Let be a functor assigning a representation to each color. For any two objects (with indexing sets and respectively) and a morphism (defined by a bijection such that the colors match), let be the induced -linear isomorphism between the tensor product spaces. For any family of vectors , the isomorphism maps the elementary tensor product to an elementary tensor product in as follows: where is the linear isomorphism induced by the color equality .
Representation homomorphism induced by
#homToRepHomLet be a field, be a group, and be a functor mapping each "color" to a representation . For any morphism in (where and represent collections of colors indexed by sets and respectively, and is a color-preserving bijection ), this definition constructs a -representation homomorphism: The underlying linear map of is the isomorphism that reindexes the factors of the tensor product into using the bijection . This map is shown to be an intertwiner, meaning it commutes with the action of on the tensor product representations.
Action of Induced Representation Homomorphism on Elementary Tensor Products
#homToRepHom_tprodLet be a field, a group, and a set of colors. Let be a functor mapping each color to a representation . For any two objects (with indexing sets and respectively) and a morphism (defined by a color-preserving bijection ), let be the induced homomorphism between the tensor product representations. Given a family of vectors for each , the action of on the elementary tensor product is given by: where is the -linear isomorphism induced by the equality of colors .
for Induced Representation Homomorphisms
#homToRepHom_idLet be a field, a group, and a set of colors. Let be a functor mapping colors to representations. For any object in the category , the representation homomorphism induced by the identity morphism on is equal to the identity morphism on the associated tensor product representation.
for Induced Representation Homomorphisms
#homToRepHom_compLet be a field, a group, and a set of colors. Let be a functor mapping colors to representations. For any objects in the category and morphisms and , the representation homomorphism induced by the composition is equal to the composition of the individual representation homomorphisms induced by and , denoted .
Representation functor induced by
#toRepFuncLet be a field, be a group, and be a set of "colors". Given a functor that assigns a representation to each color, `toRepFunc` is the functor from the category of indexed colors to the category of representations . For an object (an indexing set with a coloring map ), the functor assigns the representation: For a morphism in (a color-preserving bijection between the indexing sets), the functor assigns the representation homomorphism that reindexes the factors of the tensor product.
Unit isomorphism
#toRepUnitIsoLet be a field, be a group, and be a type of "colors". Given a functor that assigns a representation of to each color, let be the functor that maps an object in (an indexed collection of colors) to its corresponding tensor product representation. The definition `toRepUnitIso` is an isomorphism in the category of representations : where is the monoidal unit of representations (the trivial representation on ) and is the monoidal unit in (representing an empty set of indices). This isomorphism is induced by the canonical linear equivalence between the base field and the tensor product over an empty index set, .
Linear equivalence for representations on
#discreteSumEquivLet be a type of colors, a field, and a group. Given a functor that assigns a representation to each color, and two types (indexing sets) and with coloring maps and , let be an element of the disjoint union of the indexing sets. The definition `discreteSumEquiv` provides a linear equivalence between the representation associated with when viewed as an element of the individual components or , and the representation associated with via the combined coloring map . Specifically, if , the equivalence identifies with ; if , it identifies with . Since these objects are definitionally equal, the equivalence is the identity map .
Linear equivalence for representations of objects in
#μModEquivLet be a type of colors, a field, and a group. Given a functor that assigns a representation to each color, and two objects in the category , let and be the underlying -vector spaces of the representations `toRep F X` and `toRep F Y` respectively. The definition `μModEquiv` provides a -linear equivalence: where is the vector space of the representation associated with the monoidal product in . This equivalence identifies the tensor product of two -tensor products (indexed by the indexing sets of and ) with a single -tensor product indexed by the disjoint union of those sets. It is constructed by composing the standard equivalence for tensor products of -tensor products (`tmulEquiv`) with the linear equivalence that identifies the colored indices across the sum (`discreteSumEquiv`).
of a tensor product of pure tensors equals a pure tensor on the combined index set
#μModEquiv_tmul_tprodLet be a type of colors, a field, and a group. Given a functor that assigns a representation to each color, let and be objects in with indexing sets and respectively. Let and be families of vectors such that each and belong to the representations associated with the colors of the respective indices. The theorem states that the linear equivalence maps the tensor product of the pure tensors corresponding to and to a pure tensor over the disjoint union : where is the function on that returns for an element in the left summand and for an element in the right summand, and is the canonical identification of the corresponding representation spaces.
Isomorphism of representations
#μLet be a type of colors, a field, and a group. Given a functor that assigns a representation to each color, and two objects in the category , the definition is the isomorphism of representations: where and are the representations associated with and (constructed as tensor products of the representations of their constituent colors), and is the monoidal product in . This isomorphism lifts the linear equivalence between the underlying vector spaces to the category of representations, showing that the identification of indexing sets via disjoint union is compatible with the group action.
The Monoidal Isomorphism Maps the Tensor Product of Pure Tensors to a Combined Pure Tensor
#μ_tmul_tprodLet be a type of colors, a field, and a group. Given a functor that assigns a representation to each color, let and be objects in with indexing sets and . Let and be families of vectors such that each and belong to the representations associated with the colors of the respective indices. The monoidal coherence isomorphism satisfies the property that the image of the tensor product of the pure tensors for and is the pure tensor on the combined index set : where returns for and for , and is the canonical linear identification between the representation spaces.
of the tensor product of pure tensors for `OverColor.mk` objects equals a pure tensor on the combined index set
#μ_tmul_tprod_mkLet be a type of colors, a field, and a group. Let be a functor that assigns a representation to each color. For any types with coloring maps and , let and be families of vectors such that each and belong to the representations associated with their respective colors. The isomorphism between the tensor product of representations and the representation of the combined system satisfies: where is the vector if and if , and is the canonical linear equivalence between the corresponding representation spaces.
Left Naturality of the Monoidal Isomorphism for the `lift` Functor
#μ_natural_leftLet be a set of colors, a field, and a group. Let be a functor that assigns a representation to each color. For any objects in the category and a morphism , let denote the associated tensor product representation and be the representation homomorphism induced by . The monoidal natural isomorphism between the tensor product of representations and the representation of the monoidal product satisfies the left naturality condition: where denotes the composition of homomorphisms and denotes the monoidal product in the category of representations and in .
Naturality of the monoidal isomorphism in the second argument
#μ_natural_rightLet be a field, a group, and a set of colors. Let be a functor mapping each color to a representation . For any objects and a morphism (a color-preserving bijection), let be the representation formed by the tensor product of the components of , and let be the induced representation homomorphism. The monoidal coherence isomorphism satisfies the naturality condition: where denotes the composition of morphisms in the category of representations, and is the morphism in corresponding to the whisker-left operation.
Monoidal Associativity of the isomorphism for `toRep`
#associativityLet be a collection of colors, and be a functor that assigns a representation of a group over a field to each color. For any objects in the category , let be the corresponding tensor product representations in . Let be the natural isomorphism that identifies the tensor products of representations, and let be the representation homomorphism induced by a morphism in . Then the following diagram of isomorphisms commutes: where is the associator in and is the associator in the category of representations.
Left Unitality of the `toRep` Functor
#left_unitalityLet be a field, a group, and a type of colors. Given a functor that maps colors to representations, let be the induced functor that maps an indexed collection of colors to its tensor product representation. For any object , the left unitor in the category of representations is equal to the composition of: 1. The unit isomorphism , where identifies the trivial representation with the representation of the empty index set. 2. The monoidal isomorphism . 3. The representation homomorphism induced by the left unitor in the category . Mathematically, this is expressed as:
Right Unitality of the Monoidal Functor `toRep F`
#right_unitalityLet be a field, a group, and a set of colors. Given a functor that assigns a representation to each color, let be the functor that maps an indexed collection of colors to its tensor product representation. For any object , the right unitor in the category of representations satisfies the following coherence condition: where: - is the unit isomorphism mapping the trivial representation to the representation of the empty index set. - is the monoidal coherence isomorphism. - is the representation homomorphism induced by the right unitor in the category .
Let be a type of colors, a field, and a group. Given a functor that assigns a representation to each color, let and be objects in the category . The monoidal coherence isomorphism and the representation homomorphism induced by the braiding in satisfy the following compatibility relation with the braiding in the category of representations: where denotes the composition of morphisms in .
Let be a type of colors, a field, and a group. Given a functor that assigns a representation to each color, let and be objects in the category . The representation homomorphism induced by the braiding in is equal to the following composition of morphisms in : where: - is the monoidal coherence isomorphism associated with the lifting of . - is the braiding isomorphism in the category of representations . - denotes the composition of morphisms in diagrammatic order.
`toRepFunc F` is a lax braided monoidal functor
#toRepFunc_laxBraidedFunctorLet be a field, be a group, and be a set of colors. Given a functor that assigns a representation to each color, let be the induced representation functor (which maps an indexed collection of colors to the tensor product of their corresponding representations). The structure `toRepFunc_laxBraidedFunctor` defines as a lax braided monoidal functor. This structure is equipped with: 1. A unit morphism mapping the trivial representation to the representation of the empty set of indices. 2. A natural transformation for any objects . 3. The compatibility condition with the braiding : where is the braiding in and is the braiding in the category of representations. It also satisfies the standard coherence axioms for associativity and unitality.
`toRepFunc F` is a monoidal functor
#toRepFunc_monoidalFunctorLet be a field, be a group, and be a set of colors. Given a functor that assigns a representation to each color, let be the induced representation functor (which maps an indexed collection of colors to the tensor product of their corresponding representations). The structure `toRepFunc_monoidalFunctor` defines as a monoidal functor. Specifically, this means the lax monoidal structure of is strong, such that: 1. The unit morphism (mapping the trivial representation to the representation of the empty set of indices) is an isomorphism. 2. The natural transformation is an isomorphism for all objects .
`toRepFunc F` is a braided monoidal functor
#toRepFunc_braidedFunctorLet be a field, be a group, and be a set of colors. Given a functor that assigns a representation to each color, let be the induced representation functor (which maps an indexed collection of colors to the tensor product of their corresponding representations). The structure `toRepFunc_braidedFunctor` defines as a braided monoidal functor. This means that is a monoidal functor that preserves the braiding between the categories and . Specifically, for any objects , the monoidal natural transformation and the braiding satisfy: where is the braiding in (reindexing of the tensor product) and is the standard braiding in the category of representations.
Component of the lifted natural transformation at
#repNatTransOfColorAppLet be a field, be a group, and be a set of colors. Given two functors and a natural transformation , and given an object (defined by an indexing set and a coloring map ), the map is the representation homomorphism constructed as the tensor product of the morphisms . Specifically, for a pure tensor , where , the map acts as:
Action of the lifted natural transformation on pure tensors
#repNatTransOfColorApp_tprodLet be a field, be a group, and be a set of colors. Given two functors and a natural transformation , let be an object in defined by an indexing set and a coloring map . Let denote the component of the lifted natural transformation at , which is a representation homomorphism between the tensor products and . For any collection of vectors indexed by , the action of on the pure tensor is given by the tensor product of the individual components of : where is the component of the natural transformation evaluated at the color .
Naturality of the Lifted Natural Transformation
#repNatTransOfColorApp_naturalityLet be a field, be a group, and be a set of colors. Let be two functors that assign representations to colors, and let be a natural transformation between them. Let be the induced functors (denoted by `toRepFunc`) which map an object (consisting of an indexing set and coloring map ) to the tensor product representation . For any morphism in , the induced representation homomorphisms and satisfy the naturality condition with respect to the lifted natural transformation : where is the component of the lifted natural transformation at , defined by the tensor product of the maps .
Natural transformation induced by
#repNatTransOfColorLet be a field, be a group, and be a set of colors. Given two functors that assign representations to colors, and a natural transformation between them, let be the induced representation functors (as defined by `toRepFunc`). The natural transformation is defined such that for any object (an indexing set with a coloring map ), its component is the representation homomorphism: constructed as the tensor product of the morphisms .
Unit Compatibility of the Lifted Natural Transformation:
#repNatTransOfColorApp_unitLet be a field, be a group, and be a set of colors. Given two functors that assign representations to colors and a natural transformation , let be the induced representation functors (as defined by `toRepFunc`). Let and be the monoidal unit morphisms of the lax monoidal structures for and respectively, where denotes the monoidal unit in the corresponding categories. Then, the component of the lifted natural transformation at the unit object, denoted , satisfies the unit compatibility condition: where the composition is taken in the category of representations .
Monoidal Compatibility of the Lifted Natural Transformation:
#repNatTransOfColorApp_tensorLet be a field, a group, and a set of colors. Given two functors and a natural transformation , let be the representation functors induced by and (which map an indexed collection of colors to the tensor product of their corresponding representations). For any objects , let be the monoidal coherence isomorphism associated with , and let be the component of the lifted natural transformation at . The theorem states that the lifted natural transformation is compatible with the monoidal structure maps: where denotes morphism composition in the category of representations , and denotes the tensor product of morphisms.
The lifted natural transformation is monoidal
#repNatTransOfColor_isMonoidalLet be a field, a group, and a set of colors. Given two functors that assign representations to colors and a natural transformation , let be the representation functors induced by and . The natural transformation (denoted by `repNatTransOfColor η`) induced by is monoidal. Specifically, it satisfies: 1. **Unit Compatibility:** , where and are the monoidal unit morphisms. 2. **Tensor Compatibility:** for all , where and are the monoidal coherence morphisms.
Lifting functor
#liftLet be a field, be a group, and be a set of colors. The functor `lift` maps a functor (which assigns a representation to each color) to a lax braided monoidal functor . This functor acts as a section of the forgetful functor that restricts a monoidal functor to the individual colors. Specifically: 1. **Action on objects:** For a functor that assigns a representation to each color , `lift(F)` is the lax braided monoidal functor that maps a colored indexing set (where ) to the tensor product of representations . 2. **Action on morphisms:** For a natural transformation , `lift(\eta)` is the monoidal natural transformation whose components are the tensor products of the morphisms .
is a monoidal functor
#instMonoidalRepObjFunctorDiscreteLaxBraidedFunctorLet be a field, be a group, and be a set of colors. For any functor that assigns a representation to each color, the lifted functor from to (which maps a colored indexing set to the tensor product of the corresponding representations) is a monoidal functor.
is a lax braided monoidal functor
#instLaxBraidedRepObjFunctorDiscreteLaxBraidedFunctorLet be a field, be a group, and be a set of colors. For any functor that assigns a representation to each color, the induced functor (which maps an indexed collection of colors to the tensor product of their corresponding representations) is a lax braided monoidal functor. Specifically, it is equipped with a natural transformation that is compatible with the braiding such that: for all objects .
is a braided monoidal functor
#instBraidedRepObjFunctorDiscreteLaxBraidedFunctorLet be a field, be a group, and be a set of colors. For any functor that assigns a representation to each color, the induced functor (which maps a colored indexing set to the tensor product of its corresponding representations) is a braided monoidal functor. This implies that the functor commutes with the braiding isomorphisms of the monoidal categories: for any objects , the image of the braiding is equal to the braiding in the category .
Action of the Lifting Functor on Elementary Tensor Products
#map_tprodLet be a field, be a group, and be a set of colors. Let be a functor that assigns a representation to each color . Let be the induced functor from to , which maps an object (defined by an indexing set and color map ) to the tensor product representation . For any morphism in (corresponding to a color-preserving bijection ) and any elementary tensor product where , the action of the induced representation homomorphism is given by: where is the -linear isomorphism induced by the equality of colors .
Action of the Monoidal Coherence of on Elementary Tensors
#obj_μ_tprod_tmulLet be a field, be a group, and be a type of colors. Let be a functor that assigns a representation to each color. Let be the induced monoidal functor from to , which maps an object (defined by an indexing set and color map ) to the tensor product representation . For any two objects and families of vectors and (where and belong to the representations associated with the colors of their respective indices), the monoidal coherence morphism satisfies: where is the vector if and if , and is the canonical linear identification between the representation spaces.
Action of the inverse monoidal coherence of on elementary tensors
#μIso_inv_tprodLet be a field, be a group, and be a set of colors. Let be a functor that assigns a representation to each color. Let be the induced monoidal functor from to , which maps an object (with indexing set and coloring map ) to the tensor product representation . For any two objects , the inverse of the monoidal coherence isomorphism acts on an elementary tensor product (where ) by: where and are the canonical injections into the disjoint union of indexing sets.
Inverse of the monoidal structure map for
#inv_μLet be a field, be a group, and be a set of colors. Given a functor that assigns a representation to each color, let be the corresponding monoidal functor. For any two objects in , the inverse of the monoidal natural transformation component is equal to the inverse morphism of the representation isomorphism .
Inclusion functor
#inclThe functor is the natural inclusion that maps each color to an object in representing a single index colored by . Specifically, it maps to the object defined by the function from the singleton set to where .
Forgetful functor
#forgetThe forgetful functor maps a lax braided monoidal functor to a functor from the discrete category of colors to the category of representations . Specifically, for each color , the resulting functor maps to the representation , where is the natural inclusion that interprets a color as a single index. For a natural transformation , the forgetful functor produces a natural transformation whose components are those of restricted to the objects in the image of . This process ignores the monoidal structure and braiding of the source functor.
Linear equivalence for lifted representations
#forgetLiftAppVLet be a field, be a group, and be a type of colors. Given a functor that maps each color to a representation , the function `forgetLiftAppV` provides a -linear equivalence between the underlying vector space of the representation (obtained by applying the lifted functor to a singleton set colored by ) and the underlying vector space of .
`(forgetLiftAppV F c).symm x = \bigotimes_{i \in \{0\}} x`
#forgetLiftAppV_symm_applyLet be a field, be a group, and be a type of colors. Given a functor that maps each color to a representation , let be the -linear equivalence identifying the underlying vector space of the tensor product (the lifted representation of a singleton set colored by ) with the vector space . For any vector , the inverse of this linear equivalence maps to the elementary tensor product .
Isomorphism for representations of colors
#forgetLiftAppLet be a field, be a group, and be a type of colors. Given a functor that assigns a representation to each color , let be the lifted braided monoidal functor that maps a colored indexing set to the tensor product of the corresponding representations. For any color , the definition `forgetLiftApp` provides an isomorphism in the category of representations between the representation (the tensor product indexed by a singleton set colored by ) and the original representation .
Naturality of the isomorphism `forgetLiftApp` with respect to color equality
#forgetLiftApp_naturality_eqToHomLet be a field, be a group, and be a type of colors. Suppose is a functor assigning a representation to each color, and let be the associated lifted braided monoidal functor. For any color , let denote the isomorphism `forgetLiftApp`, which identifies the representation of a singleton set colored by with the representation . For any colors and an equality , the following diagram in commutes: where is the morphism in induced by the equality, and is the corresponding isomorphism in .
Element-wise naturality of under color equality
#forgetLiftApp_naturality_eqToHom_applyLet be a field, be a group, and be a type of colors. Suppose is a functor that assigns a representation to each color, and let be the associated lifted braided monoidal functor. For any color , let denote the isomorphism `forgetLiftApp`, which identifies the representation of a singleton set colored by with the representation . For any colors , an equality , and any vector , the following equality holds in : where is the morphism in induced by the color equality in the discrete category, and is the induced isomorphism between colored singleton sets in .
Let be a field, be a group, and be a type of colors. Suppose is a functor mapping each color to a representation . Let be the lifted braided monoidal functor that maps a singleton set colored by to the tensor product representation . Let be the canonical isomorphism in the category of representations. For any vector and , the underlying linear map of the isomorphism maps to if and only if is the elementary tensor .
Isomorphism for colored representations
#forgetLiftAppConLet be a field, be a group, and be a type of colors. Given a functor that assigns a representation to each color , let be the lifted braided monoidal functor that maps a colored indexing set to the tensor product of the corresponding representations. For any color , the definition `forgetLiftAppCon` provides an isomorphism in the category of representations between the representation (where is the colored indexing set containing a single element with color ) and the original representation .
Expansion of using and the singleton isomorphism
#forgetLiftAppCon_inv_apply_expandLet be a field, be a group, and be a type of colors. Let be a functor that assigns a representation to each color , and let be the lifted braided monoidal functor that maps a colored indexing set to the tensor product of its components. Consider two ways to represent a singleton indexing set colored by : one via a function (mapping the unique element to ) and one via a vector notation . Let and be the corresponding canonical isomorphisms in the category of representations. For any color and vector in the representation , the application of the inverse of to is equal to applying the inverse of to and then applying the representation homomorphism , where is the isomorphism between the two singleton colored sets induced by the extensionality of the color mapping.
Naturality of the isomorphism with respect to color equality
#forgetLiftAppCon_naturality_eqToHomLet be a type of colors, a field, and a group. Given a functor and its lifted braided monoidal functor , let denote the isomorphism `forgetLiftAppCon` for a color . For any colors and an equality , the following diagram in the category of representations commutes: where and are the morphisms induced by the equality in the categories and , respectively.
Naturality of the isomorphism for elements under color equality
#forgetLiftAppCon_naturality_eqToHom_applyLet be a field, be a group, and be a type of colors. Let be a functor that assigns a representation to each color, and let be the lifted braided monoidal functor that maps a colored indexing set to the tensor product of its components. For any color , let be the canonical isomorphism (defined as `forgetLiftAppCon`) between the representation of the singleton set and the original representation . Given two colors such that (denoted by the equality ), and an element in the representation , the following identity holds: where and are the morphisms (linear maps) induced by the equality in the respective categories.
Natural isomorphism \( \text{forget} \circ \text{lift} \cong \text{Id} \) for color-to-representation lifting
#forgetLiftLet \( C \) be a type (representing a set of "colors" or indices), \( k \) a field, and \( G \) a group. Let \( \text{Rep } k G \) denote the category of representations of \( G \) over \( k \). There exists a functor \( \text{lift} \) that extends an assignment of representations to colors \( F : \text{Discrete } C \to \text{Rep } k G \) to a braided monoidal functor from the category of colored strings \( \text{OverColor } C \) to \( \text{Rep } k G \). Let \( \text{forget} \) be the forgetful functor that restricts a braided monoidal functor \( \text{OverColor } C \to \text{Rep } k G \) back to its values on the discrete category of colors. This definition provides the natural isomorphism \( \text{forget} \circ \text{lift} \cong \text{Id} \), confirming that \( \text{lift} \) is a section of the forgetful functor.
