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Mathlib.AlgebraicTopology.SimplicialObject.Basic

Simplicial objects in a category. #

A simplicial object in a category C is a C-valued presheaf on SimplexCategory. (Similarly a cosimplicial object is functor SimplexCategory ⥤ C.)

Use the notation X _[n] in the Simplicial locale to obtain the n-th term of a (co)simplicial object X, where n is a natural number.

The category of simplicial objects valued in a category C. This is the category of contravariant functors from SimplexCategory to C.

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      X _[n] denotes the nth-term of the simplicial object X

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        Face maps for a simplicial object.

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          Degeneracy maps for a simplicial object.

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            The diagonal of a simplex is the long edge of the simplex.

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              Isomorphisms from identities in ℕ.

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                The generic case of the first simplicial identity

                theorem CategoryTheory.SimplicialObject.δ_comp_δ' {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) {n : } {i : Fin (n + 2)} {j : Fin (n + 3)} (H : i.castSucc < j) :
                CategoryTheory.CategoryStruct.comp (X j) (X i) = CategoryTheory.CategoryStruct.comp (X i.castSucc) (X (j.pred ))
                theorem CategoryTheory.SimplicialObject.δ_comp_δ'' {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) {n : } {i : Fin (n + 3)} {j : Fin (n + 2)} (H : i j.castSucc) :
                CategoryTheory.CategoryStruct.comp (X j.succ) (X (i.castLT )) = CategoryTheory.CategoryStruct.comp (X i) (X j)

                The special case of the first simplicial identity

                theorem CategoryTheory.SimplicialObject.δ_comp_σ_of_le {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) {n : } {i : Fin (n + 2)} {j : Fin (n + 1)} (H : i j.castSucc) :
                CategoryTheory.CategoryStruct.comp (X j.succ) (X i.castSucc) = CategoryTheory.CategoryStruct.comp (X i) (X j)

                The second simplicial identity

                theorem CategoryTheory.SimplicialObject.δ_comp_σ_of_gt {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) {n : } {i : Fin (n + 2)} {j : Fin (n + 1)} (H : j.castSucc < i) :
                CategoryTheory.CategoryStruct.comp (X j.castSucc) (X i.succ) = CategoryTheory.CategoryStruct.comp (X i) (X j)

                The fourth simplicial identity

                theorem CategoryTheory.SimplicialObject.δ_comp_σ_of_gt' {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) {n : } {i : Fin (n + 3)} {j : Fin (n + 2)} (H : j.succ < i) :
                CategoryTheory.CategoryStruct.comp (X j) (X i) = CategoryTheory.CategoryStruct.comp (X (i.pred )) (X (j.castLT ))

                The fifth simplicial identity

                Since Truncated.inclusion is fully faithful, so is right Kan extension along it.

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                  Since Truncated.inclusion is fully faithful, so is left Kan extension along it.

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                    theorem CategoryTheory.SimplicialObject.Augmented.hom_ext {C : Type u} [CategoryTheory.Category.{v, u} C] {X Y : CategoryTheory.SimplicialObject.Augmented C} (f g : X Y) (h₁ : f.left = g.left) (h₂ : f.right = g.right) :
                    f = g
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                    The functor from augmented objects to arrows.

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                      theorem CategoryTheory.SimplicialObject.Augmented.toArrow_map_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X✝ Y✝ : CategoryTheory.SimplicialObject.Augmented C} (η : X✝ Y✝) :
                      (CategoryTheory.SimplicialObject.Augmented.toArrow.map η).left = (CategoryTheory.SimplicialObject.Augmented.drop.map η).app (Opposite.op (SimplexCategory.mk 0))
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                      theorem CategoryTheory.SimplicialObject.Augmented.toArrow_map_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X✝ Y✝ : CategoryTheory.SimplicialObject.Augmented C} (η : X✝ Y✝) :
                      (CategoryTheory.SimplicialObject.Augmented.toArrow.map η).right = CategoryTheory.SimplicialObject.Augmented.point.map η
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                      theorem CategoryTheory.SimplicialObject.Augmented.toArrow_obj_hom {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject.Augmented C) :
                      (CategoryTheory.SimplicialObject.Augmented.toArrow.obj X).hom = X.hom.app (Opposite.op (SimplexCategory.mk 0))
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                      theorem CategoryTheory.SimplicialObject.Augmented.toArrow_obj_right {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject.Augmented C) :
                      (CategoryTheory.SimplicialObject.Augmented.toArrow.obj X).right = CategoryTheory.SimplicialObject.Augmented.point.obj X
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                      theorem CategoryTheory.SimplicialObject.Augmented.toArrow_obj_left {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject.Augmented C) :
                      (CategoryTheory.SimplicialObject.Augmented.toArrow.obj X).left = (CategoryTheory.SimplicialObject.Augmented.drop.obj X).obj (Opposite.op (SimplexCategory.mk 0))
                      theorem CategoryTheory.SimplicialObject.Augmented.w₀ {C : Type u} [CategoryTheory.Category.{v, u} C] {X Y : CategoryTheory.SimplicialObject.Augmented C} (f : X Y) :
                      CategoryTheory.CategoryStruct.comp ((CategoryTheory.SimplicialObject.Augmented.drop.map f).app (Opposite.op (SimplexCategory.mk 0))) (Y.hom.app (Opposite.op (SimplexCategory.mk 0))) = CategoryTheory.CategoryStruct.comp (X.hom.app (Opposite.op (SimplexCategory.mk 0))) (CategoryTheory.SimplicialObject.Augmented.point.map f)

                      The compatibility of a morphism with the augmentation, on 0-simplices

                      Functor composition induces a functor on augmented simplicial objects.

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                        Functor composition induces a functor on augmented simplicial objects.

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                          theorem CategoryTheory.SimplicialObject.Augmented.whiskering_map_app_right (C : Type u) [CategoryTheory.Category.{v, u} C] (D : Type u') [CategoryTheory.Category.{v', u'} D] {X✝ Y✝ : CategoryTheory.Functor C D} (η : X✝ Y✝) (A : CategoryTheory.SimplicialObject.Augmented C) :
                          (((CategoryTheory.SimplicialObject.Augmented.whiskering C D).map η).app A).right = η.app (CategoryTheory.SimplicialObject.Augmented.point.obj A)

                          Augment a simplicial object with an object.

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                            theorem CategoryTheory.SimplicialObject.augment_hom_app {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) (X₀ : C) (f : X.obj (Opposite.op (SimplexCategory.mk 0)) X₀) (w : ∀ (i : SimplexCategory) (g₁ g₂ : SimplexCategory.mk 0 i), CategoryTheory.CategoryStruct.comp (X.map g₁.op) f = CategoryTheory.CategoryStruct.comp (X.map g₂.op) f) (x✝ : SimplexCategoryᵒᵖ) :
                            (X.augment X₀ f w).hom.app x✝ = CategoryTheory.CategoryStruct.comp (X.map ((SimplexCategory.mk 0).const (Opposite.unop x✝) 0).op) f
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                            theorem CategoryTheory.SimplicialObject.augment_right {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) (X₀ : C) (f : X.obj (Opposite.op (SimplexCategory.mk 0)) X₀) (w : ∀ (i : SimplexCategory) (g₁ g₂ : SimplexCategory.mk 0 i), CategoryTheory.CategoryStruct.comp (X.map g₁.op) f = CategoryTheory.CategoryStruct.comp (X.map g₂.op) f) :
                            (X.augment X₀ f w).right = X₀
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                            theorem CategoryTheory.SimplicialObject.augment_left {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject C) (X₀ : C) (f : X.obj (Opposite.op (SimplexCategory.mk 0)) X₀) (w : ∀ (i : SimplexCategory) (g₁ g₂ : SimplexCategory.mk 0 i), CategoryTheory.CategoryStruct.comp (X.map g₁.op) f = CategoryTheory.CategoryStruct.comp (X.map g₂.op) f) :
                            (X.augment X₀ f w).left = X

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                              X _[n] denotes the nth-term of the cosimplicial object X

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                                Coface maps for a cosimplicial object.

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                                  Codegeneracy maps for a cosimplicial object.

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                                    Isomorphisms from identities in ℕ.

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                                      The generic case of the first cosimplicial identity

                                      theorem CategoryTheory.CosimplicialObject.δ_comp_δ' {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) {n : } {i : Fin (n + 2)} {j : Fin (n + 3)} (H : i.castSucc < j) :
                                      CategoryTheory.CategoryStruct.comp (X i) (X j) = CategoryTheory.CategoryStruct.comp (X (j.pred )) (X i.castSucc)
                                      theorem CategoryTheory.CosimplicialObject.δ_comp_δ'' {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) {n : } {i : Fin (n + 3)} {j : Fin (n + 2)} (H : i j.castSucc) :
                                      CategoryTheory.CategoryStruct.comp (X (i.castLT )) (X j.succ) = CategoryTheory.CategoryStruct.comp (X j) (X i)

                                      The special case of the first cosimplicial identity

                                      theorem CategoryTheory.CosimplicialObject.δ_comp_σ_of_le {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) {n : } {i : Fin (n + 2)} {j : Fin (n + 1)} (H : i j.castSucc) :
                                      CategoryTheory.CategoryStruct.comp (X i.castSucc) (X j.succ) = CategoryTheory.CategoryStruct.comp (X j) (X i)

                                      The second cosimplicial identity

                                      The first part of the third cosimplicial identity

                                      theorem CategoryTheory.CosimplicialObject.δ_comp_σ_of_gt {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) {n : } {i : Fin (n + 2)} {j : Fin (n + 1)} (H : j.castSucc < i) :
                                      CategoryTheory.CategoryStruct.comp (X i.succ) (X j.castSucc) = CategoryTheory.CategoryStruct.comp (X j) (X i)

                                      The fourth cosimplicial identity

                                      theorem CategoryTheory.CosimplicialObject.δ_comp_σ_of_gt' {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) {n : } {i : Fin (n + 3)} {j : Fin (n + 2)} (H : j.succ < i) :
                                      CategoryTheory.CategoryStruct.comp (X i) (X j) = CategoryTheory.CategoryStruct.comp (X (j.castLT )) (X (i.pred ))

                                      The fifth cosimplicial identity

                                      theorem CategoryTheory.CosimplicialObject.Augmented.hom_ext {C : Type u} [CategoryTheory.Category.{v, u} C] {X Y : CategoryTheory.CosimplicialObject.Augmented C} (f g : X Y) (h₁ : f.left = g.left) (h₂ : f.right = g.right) :
                                      f = g

                                      The functor from augmented objects to arrows.

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                                        theorem CategoryTheory.CosimplicialObject.Augmented.toArrow_map_left {C : Type u} [CategoryTheory.Category.{v, u} C] {X✝ Y✝ : CategoryTheory.CosimplicialObject.Augmented C} (η : X✝ Y✝) :
                                        (CategoryTheory.CosimplicialObject.Augmented.toArrow.map η).left = η.left
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                                        theorem CategoryTheory.CosimplicialObject.Augmented.toArrow_obj_left {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject.Augmented C) :
                                        (CategoryTheory.CosimplicialObject.Augmented.toArrow.obj X).left = X.left
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                                        theorem CategoryTheory.CosimplicialObject.Augmented.toArrow_map_right {C : Type u} [CategoryTheory.Category.{v, u} C] {X✝ Y✝ : CategoryTheory.CosimplicialObject.Augmented C} (η : X✝ Y✝) :
                                        (CategoryTheory.CosimplicialObject.Augmented.toArrow.map η).right = η.right.app (SimplexCategory.mk 0)
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                                        theorem CategoryTheory.CosimplicialObject.Augmented.toArrow_obj_hom {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject.Augmented C) :
                                        (CategoryTheory.CosimplicialObject.Augmented.toArrow.obj X).hom = X.hom.app (SimplexCategory.mk 0)
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                                        theorem CategoryTheory.CosimplicialObject.Augmented.toArrow_obj_right {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject.Augmented C) :
                                        (CategoryTheory.CosimplicialObject.Augmented.toArrow.obj X).right = X.right.obj (SimplexCategory.mk 0)

                                        Functor composition induces a functor on augmented cosimplicial objects.

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                                          Functor composition induces a functor on augmented cosimplicial objects.

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                                            theorem CategoryTheory.CosimplicialObject.Augmented.whiskering_map_app_left (C : Type u) [CategoryTheory.Category.{v, u} C] (D : Type u') [CategoryTheory.Category.{v', u'} D] {X✝ Y✝ : CategoryTheory.Functor C D} (η : X✝ Y✝) (A : CategoryTheory.CosimplicialObject.Augmented C) :
                                            (((CategoryTheory.CosimplicialObject.Augmented.whiskering C D).map η).app A).left = η.app (CategoryTheory.CosimplicialObject.Augmented.point.obj A)

                                            Augment a cosimplicial object with an object.

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                                              theorem CategoryTheory.CosimplicialObject.augment_left {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) (X₀ : C) (f : X₀ X.obj (SimplexCategory.mk 0)) (w : ∀ (i : SimplexCategory) (g₁ g₂ : SimplexCategory.mk 0 i), CategoryTheory.CategoryStruct.comp f (X.map g₁) = CategoryTheory.CategoryStruct.comp f (X.map g₂)) :
                                              (X.augment X₀ f w).left = X₀
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                                              theorem CategoryTheory.CosimplicialObject.augment_hom_app {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) (X₀ : C) (f : X₀ X.obj (SimplexCategory.mk 0)) (w : ∀ (i : SimplexCategory) (g₁ g₂ : SimplexCategory.mk 0 i), CategoryTheory.CategoryStruct.comp f (X.map g₁) = CategoryTheory.CategoryStruct.comp f (X.map g₂)) (x✝ : SimplexCategory) :
                                              (X.augment X₀ f w).hom.app x✝ = CategoryTheory.CategoryStruct.comp f (X.map ((SimplexCategory.mk 0).const x✝ 0))
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                                              theorem CategoryTheory.CosimplicialObject.augment_right {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.CosimplicialObject C) (X₀ : C) (f : X₀ X.obj (SimplexCategory.mk 0)) (w : ∀ (i : SimplexCategory) (g₁ g₂ : SimplexCategory.mk 0 i), CategoryTheory.CategoryStruct.comp f (X.map g₁) = CategoryTheory.CategoryStruct.comp f (X.map g₂)) :
                                              (X.augment X₀ f w).right = X
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                                              Construct an augmented cosimplicial object in the opposite category from an augmented simplicial object.

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                                                theorem CategoryTheory.SimplicialObject.Augmented.rightOp_right_map {C : Type u} [CategoryTheory.Category.{v, u} C] (X : CategoryTheory.SimplicialObject.Augmented C) {X✝ Y✝ : SimplexCategory} (f : X✝ Y✝) :
                                                X.rightOp.right.map f = (X.left.map f.op).op

                                                Construct an augmented simplicial object from an augmented cosimplicial object in the opposite category.

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                                                  Converting an augmented simplicial object to an augmented cosimplicial object and back is isomorphic to the given object.

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                                                    Converting an augmented cosimplicial object to an augmented simplicial object and back is isomorphic to the given object.

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                                                      A functorial version of Cosimplicial_object.Augmented.leftOp.

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                                                        The contravariant categorical equivalence between augmented simplicial objects and augmented cosimplicial objects in the opposite category.

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