Documentation

Mathlib.CategoryTheory.GradedObject

The category of graded objects #

For any type β, a β-graded object over some category C is just a function β → C into the objects of C. We put the "pointwise" category structure on these, as the non-dependent specialization of CategoryTheory.Pi.

We describe the comap functors obtained by precomposing with functions β → γ.

As a consequence a fixed element (e.g. 1) in an additive group β provides a shift functor on β-graded objects

When C has coproducts we construct the total functor GradedObject β C ⥤ C, show that it is faithful, and deduce that when C is concrete so is GradedObject β C.

A covariant functoriality of GradedObject β C with respect to the index set β is also introduced: if p : I → J is a map such that C has coproducts indexed by p ⁻¹' {j}, we have a functor map : GradedObject I C ⥤ GradedObject J C.

def CategoryTheory.GradedObject (β : Type w) (C : Type u) :
Type (max w u)

A type synonym for β → C, used for β-graded objects in a category C.

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    abbrev CategoryTheory.GradedObjectWithShift {β : Type w} [AddCommGroup β] :
    βType u → Type (max w u)

    A type synonym for β → C, used for β-graded objects in a category C with a shift functor given by translation by s.

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      theorem CategoryTheory.GradedObject.categoryOfGradedObjects_comp {C : Type u} [CategoryTheory.Category.{v, u} C] (β : Type w) :
      ∀ {X Y Z : (i : β) → (fun (x : β) => C) i} (f : X Y) (g : Y Z) (i : β), CategoryTheory.CategoryStruct.comp f g i = CategoryTheory.CategoryStruct.comp (f i) (g i)
      theorem CategoryTheory.GradedObject.hom_ext {C : Type u} [CategoryTheory.Category.{v, u} C] {β : Type u_1} {X : CategoryTheory.GradedObject β C} {Y : CategoryTheory.GradedObject β C} (f : X Y) (g : X Y) (h : ∀ (x : β), f x = g x) :
      f = g
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      The projection of a graded object to its i-th component.

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        theorem CategoryTheory.GradedObject.isoMk_inv {C : Type u} [CategoryTheory.Category.{v, u} C] {β : Type u_1} (X : CategoryTheory.GradedObject β C) (Y : CategoryTheory.GradedObject β C) (e : (i : β) → X i Y i) (i : β) :
        (CategoryTheory.GradedObject.isoMk X Y e).inv i = (e i).inv
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        theorem CategoryTheory.GradedObject.isoMk_hom {C : Type u} [CategoryTheory.Category.{v, u} C] {β : Type u_1} (X : CategoryTheory.GradedObject β C) (Y : CategoryTheory.GradedObject β C) (e : (i : β) → X i Y i) (i : β) :
        (CategoryTheory.GradedObject.isoMk X Y e).hom i = (e i).hom
        def CategoryTheory.GradedObject.isoMk {C : Type u} [CategoryTheory.Category.{v, u} C] {β : Type u_1} (X : CategoryTheory.GradedObject β C) (Y : CategoryTheory.GradedObject β C) (e : (i : β) → X i Y i) :
        X Y

        Constructor for isomorphisms in GradedObject

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          Pull back an I-graded object in C to a J-graded object along a function J → I.

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            theorem CategoryTheory.GradedObject.comapEq_inv_app (C : Type u) [CategoryTheory.Category.{v, u} C] {β : Type w} {γ : Type w} {f : βγ} {g : βγ} (h : f = g) (X : CategoryTheory.GradedObject γ C) (b : β) :
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            theorem CategoryTheory.GradedObject.comapEq_hom_app (C : Type u) [CategoryTheory.Category.{v, u} C] {β : Type w} {γ : Type w} {f : βγ} {g : βγ} (h : f = g) (X : CategoryTheory.GradedObject γ C) (b : β) :

            The natural isomorphism comparing between pulling back along two propositionally equal functions.

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              theorem CategoryTheory.GradedObject.eqToHom_apply (C : Type u) [CategoryTheory.Category.{v, u} C] {β : Type w} {X : βC} {Y : βC} (h : X = Y) (b : β) :

              The equivalence between β-graded objects and γ-graded objects, given an equivalence between β and γ.

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                theorem CategoryTheory.GradedObject.shiftFunctor_obj_apply {C : Type u} [CategoryTheory.Category.{v, u} C] {β : Type u_1} [AddCommGroup β] (s : β) (X : βC) (t : β) (n : ) :

                The total object of a graded object is the coproduct of the graded components.

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                  The total functor taking a graded object to the coproduct of its graded components is faithful. To prove this, we need to know that the coprojections into the coproduct are monomorphisms, which follows from the fact we have zero morphisms and decidable equality for the grading.

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                  abbrev CategoryTheory.GradedObject.mapObjFun {I : Type u_1} {J : Type u_2} {C : Type u_4} (X : CategoryTheory.GradedObject I C) (p : IJ) (j : J) (i : (p ⁻¹' {j})) :
                  C

                  If X : GradedObject I C and p : I → J, X.mapObjFun p j is the family of objects X i for i : I such that p i = j.

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                    Given X : GradedObject I C and p : I → J, X.HasMap p is the condition that for all j : J, the coproduct of all X i such p i = j exists.

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                      Given X : GradedObject I C and p : I → J, X.mapObj p is the graded object by J which in degree j consists of the coproduct of the X i such that p i = j.

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                        noncomputable def CategoryTheory.GradedObject.ιMapObj {I : Type u_1} {J : Type u_2} {C : Type u_4} [CategoryTheory.Category.{u_5, u_4} C] (X : CategoryTheory.GradedObject I C) (p : IJ) [CategoryTheory.GradedObject.HasMap X p] (i : I) (j : J) (hij : p i = j) :

                        The canonical inclusion X i ⟶ X.mapObj p j when i : I and j : J are such that p i = j.

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                          abbrev CategoryTheory.GradedObject.CofanMapObjFun {I : Type u_1} {J : Type u_2} {C : Type u_4} [CategoryTheory.Category.{u_5, u_4} C] (X : CategoryTheory.GradedObject I C) (p : IJ) (j : J) :
                          Type (max (max u_4 u_5) u_1)

                          Given X : GradedObject I C, p : I → J and j : J, CofanMapObjFun X p j is the type Cofan (X.mapObjFun p j). The point object of such colimits cofans are isomorphic to X.mapObj p j, see CofanMapObjFun.iso.

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                            def CategoryTheory.GradedObject.CofanMapObjFun.mk {I : Type u_1} {J : Type u_2} {C : Type u_4} [CategoryTheory.Category.{u_5, u_4} C] (X : CategoryTheory.GradedObject I C) (p : IJ) (j : J) (pt : C) (ι' : (i : I) → p i = j(X i pt)) :

                            Constructor for CofanMapObjFun X p j.

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                              The tautological cofan corresponding to the coproduct decomposition of X.mapObj p j.

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                                Given X : GradedObject I C, p : I → J and j : J, X.mapObj p j satisfies the universal property of the coproduct of those X i such that p i = j.

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                                  noncomputable def CategoryTheory.GradedObject.descMapObj {I : Type u_1} {J : Type u_2} {C : Type u_4} [CategoryTheory.Category.{u_5, u_4} C] (X : CategoryTheory.GradedObject I C) (p : IJ) [CategoryTheory.GradedObject.HasMap X p] {A : C} {j : J} (φ : (i : I) → p i = j(X i A)) :

                                  This is the morphism X.mapObj p j ⟶ A constructed from a family of morphisms X i ⟶ A for all i : I such that p i = j.

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                                    theorem CategoryTheory.GradedObject.ι_descMapObj {I : Type u_1} {J : Type u_2} {C : Type u_4} [CategoryTheory.Category.{u_5, u_4} C] (X : CategoryTheory.GradedObject I C) (p : IJ) [CategoryTheory.GradedObject.HasMap X p] {A : C} {j : J} (φ : (i : I) → p i = j(X i A)) (i : I) (hi : p i = j) :

                                    The canonical morphism of J-graded objects X.mapObj p ⟶ Y.mapObj p induced by a morphism X ⟶ Y of I-graded objects and a map p : I → J.

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                                      The isomorphism of J-graded objects X.mapObj p ≅ Y.mapObj p induced by an isomorphism X ≅ Y of graded objects and a map p : I → J.

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                                        Given a map p : I → J, this is the functor GradedObject I C ⥤ GradedObject J C which sends an I-object X to the graded object X.mapObj p which in degree j : J is given by the coproduct of those X i such that p i = j.

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                                          def CategoryTheory.GradedObject.cofanMapObjComp {I : Type u_1} {J : Type u_2} {K : Type u_3} {C : Type u_4} [CategoryTheory.Category.{u_5, u_4} C] (X : CategoryTheory.GradedObject I C) (p : IJ) (q : JK) (r : IK) (hpqr : ∀ (i : I), q (p i) = r i) (k : K) (c : (j : J) → q j = kCategoryTheory.GradedObject.CofanMapObjFun X p j) (c' : CategoryTheory.Limits.Cofan fun (j : (q ⁻¹' {k})) => (c j ).pt) :

                                          Given maps p : I → J, q : J → K and r : I → K such that q.comp p = r, X : GradedObject I C, k : K, the datum of cofans X.CofanMapObjFun p j for all j : J and of a cofan for all the points of these cofans, this is a cofan of type X.CofanMapObjFun r k, which is a colimit (see isColimitCofanMapObjComp) if the given cofans are.

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                                            def CategoryTheory.GradedObject.isColimitCofanMapObjComp {I : Type u_1} {J : Type u_2} {K : Type u_3} {C : Type u_4} [CategoryTheory.Category.{u_5, u_4} C] (X : CategoryTheory.GradedObject I C) (p : IJ) (q : JK) (r : IK) (hpqr : ∀ (i : I), q (p i) = r i) (k : K) (c : (j : J) → q j = kCategoryTheory.GradedObject.CofanMapObjFun X p j) (hc : (j : J) → (hj : q j = k) → CategoryTheory.Limits.IsColimit (c j hj)) (c' : CategoryTheory.Limits.Cofan fun (j : (q ⁻¹' {k})) => (c j ).pt) (hc' : CategoryTheory.Limits.IsColimit c') :

                                            Given maps p : I → J, q : J → K and r : I → K such that q.comp p = r, X : GradedObject I C, k : K, the cofan constructed by cofanMapObjComp is a colimit. In other words, if we have, for all j : J such that hj : q j = k, a colimit cofan c j hj which computes the coproduct of the X i such that p i = j, and also a colimit cofan which computes the coproduct of the points of these c j hj, then the point of this latter cofan computes the coproduct of the X i such that r i = k.

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                                              The canonical inclusion X i ⟶ X.mapObj p j when p i = j, the zero morphism otherwise.

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