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algebraic_topology.simplicial_object

Simplicial objects in a category. #

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

Face maps for a simplicial object.

Equations

Degeneracy maps for a simplicial object.

Equations

The generic case of the first simplicial identity

theorem category_theory.simplicial_object.δ_comp_δ_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i j : fin (n + 2)} (H : i ≤ j) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk n)) ⟶ X') :
X.δ j.succ ≫ X.δ i ≫ f' = X.δ (⇑fin.cast_succ i) ≫ X.δ j ≫ f'
theorem category_theory.simplicial_object.δ_comp_δ'_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i : fin (n + 2)} {j : fin (n + 3)} (H : ⇑fin.cast_succ i < j) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk n)) ⟶ X') :
X.δ j ≫ X.δ i ≫ f' = X.δ (⇑fin.cast_succ i) ≫ X.δ (j.pred _) ≫ f'
theorem category_theory.simplicial_object.δ_comp_δ''_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i : fin (n + 3)} {j : fin (n + 2)} (H : i ≤ ⇑fin.cast_succ j) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk n)) ⟶ X') :
X.δ j.succ ≫ X.δ (i.cast_lt _) ≫ f' = X.δ i ≫ X.δ j ≫ f'
theorem category_theory.simplicial_object.δ_comp_δ'' {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i : fin (n + 3)} {j : fin (n + 2)} (H : i ≤ ⇑fin.cast_succ j) :
X.δ j.succ ≫ X.δ (i.cast_lt _) = X.δ i ≫ X.δ j

The special case of the first simplicial identity

theorem category_theory.simplicial_object.δ_comp_δ_self'_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {j : fin (n + 3)} {i : fin (n + 2)} (H : j = ⇑fin.cast_succ i) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk n)) ⟶ X') :
X.δ j ≫ X.δ i ≫ f' = X.δ i.succ ≫ X.δ i ≫ f'

The second simplicial identity

theorem category_theory.simplicial_object.δ_comp_σ_of_le_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i : fin (n + 2)} {j : fin (n + 1)} (H : i ≤ ⇑fin.cast_succ j) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk (n + 1))) ⟶ X') :
X.σ j.succ ≫ X.δ (⇑fin.cast_succ i) ≫ f' = X.δ i ≫ X.σ j ≫ f'

The first part of the third simplicial identity

theorem category_theory.simplicial_object.δ_comp_σ_self'_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {j : fin (n + 2)} {i : fin (n + 1)} (H : j = ⇑fin.cast_succ i) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk n)) ⟶ X') :
X.σ i ≫ X.δ j ≫ f' = f'

The second part of the third simplicial identity

theorem category_theory.simplicial_object.δ_comp_σ_succ'_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {j : fin (n + 2)} {i : fin (n + 1)} (H : j = i.succ) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk n)) ⟶ X') :
X.σ i ≫ X.δ j ≫ f' = f'
theorem category_theory.simplicial_object.δ_comp_σ_of_gt_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i : fin (n + 2)} {j : fin (n + 1)} (H : ⇑fin.cast_succ j < i) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk (n + 1))) ⟶ X') :
X.σ (⇑fin.cast_succ j) ≫ X.δ i.succ ≫ f' = X.δ i ≫ X.σ j ≫ f'

The fourth simplicial identity

theorem category_theory.simplicial_object.δ_comp_σ_of_gt'_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i : fin (n + 3)} {j : fin (n + 2)} (H : j.succ < i) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk (n + 1))) ⟶ X') :
X.σ j ≫ X.δ i ≫ f' = X.δ (i.pred _) ≫ X.σ (j.cast_lt _) ≫ f'
theorem category_theory.simplicial_object.δ_comp_σ_of_gt' {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i : fin (n + 3)} {j : fin (n + 2)} (H : j.succ < i) :
X.σ j ≫ X.δ i = X.δ (i.pred _) ≫ X.σ (j.cast_lt _)
theorem category_theory.simplicial_object.σ_comp_σ_assoc {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) {n : ℕ} {i j : fin (n + 1)} (H : i ≤ j) {X' : C} (f' : X.obj (opposite.op (simplex_category.mk (n + 1 + 1))) ⟶ X') :
X.σ j ≫ X.σ (⇑fin.cast_succ i) ≫ f' = X.σ i ≫ X.σ j.succ ≫ f'

The fifth simplicial identity

@[simp]
@[reducible]

The constant simplicial object is the constant functor.

@[nolint]

The category of augmented simplicial objects, defined as a comma category.

Equations
Instances for category_theory.simplicial_object.augmented
@[simp]
theorem category_theory.simplicial_object.augment_left {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) (X₀ : C) (f : X.obj (opposite.op (simplex_category.mk 0)) ⟶ X₀) (w : ∀ (i : simplex_category) (g₁ g₂ : simplex_category.mk 0 ⟶ i), X.map g₁.op ≫ f = X.map g₂.op ≫ f) :
(X.augment X₀ f w).left = X

Augment a simplicial object with an object.

Equations
@[simp]
theorem category_theory.simplicial_object.augment_right {C : Type u} [category_theory.category C] (X : category_theory.simplicial_object C) (X₀ : C) (f : X.obj (opposite.op (simplex_category.mk 0)) ⟶ X₀) (w : ∀ (i : simplex_category) (g₁ g₂ : simplex_category.mk 0 ⟶ i), X.map g₁.op ≫ f = X.map g₂.op ≫ f) :
(X.augment X₀ f w).right = X₀
@[simp]

Coface maps for a cosimplicial object.

Equations

Codegeneracy maps for a cosimplicial object.

Equations

The generic case of the first cosimplicial identity

theorem category_theory.cosimplicial_object.δ_comp_δ_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i j : fin (n + 2)} (H : i ≤ j) {X' : C} (f' : X.obj (simplex_category.mk (n + 1 + 1)) ⟶ X') :
X.δ i ≫ X.δ j.succ ≫ f' = X.δ j ≫ X.δ (⇑fin.cast_succ i) ≫ f'
theorem category_theory.cosimplicial_object.δ_comp_δ'_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i : fin (n + 2)} {j : fin (n + 3)} (H : ⇑fin.cast_succ i < j) {X' : C} (f' : X.obj (simplex_category.mk (n + 1 + 1)) ⟶ X') :
X.δ i ≫ X.δ j ≫ f' = X.δ (j.pred _) ≫ X.δ (⇑fin.cast_succ i) ≫ f'
theorem category_theory.cosimplicial_object.δ_comp_δ''_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i : fin (n + 3)} {j : fin (n + 2)} (H : i ≤ ⇑fin.cast_succ j) {X' : C} (f' : X.obj (simplex_category.mk (n + 1 + 1)) ⟶ X') :
X.δ (i.cast_lt _) ≫ X.δ j.succ ≫ f' = X.δ j ≫ X.δ i ≫ f'

The special case of the first cosimplicial identity

theorem category_theory.cosimplicial_object.δ_comp_δ_self'_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i : fin (n + 2)} {j : fin (n + 3)} (H : j = ⇑fin.cast_succ i) {X' : C} (f' : X.obj (simplex_category.mk (n + 1 + 1)) ⟶ X') :
X.δ i ≫ X.δ j ≫ f' = X.δ i ≫ X.δ i.succ ≫ f'
theorem category_theory.cosimplicial_object.δ_comp_σ_of_le_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i : fin (n + 2)} {j : fin (n + 1)} (H : i ≤ ⇑fin.cast_succ j) {X' : C} (f' : X.obj (simplex_category.mk (n + 1)) ⟶ X') :
X.δ (⇑fin.cast_succ i) ≫ X.σ j.succ ≫ f' = X.σ j ≫ X.δ i ≫ f'

The second cosimplicial identity

The first part of the third cosimplicial identity

theorem category_theory.cosimplicial_object.δ_comp_σ_self'_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {j : fin (n + 2)} {i : fin (n + 1)} (H : j = ⇑fin.cast_succ i) {X' : C} (f' : X.obj (simplex_category.mk n) ⟶ X') :
X.δ j ≫ X.σ i ≫ f' = f'

The second part of the third cosimplicial identity

theorem category_theory.cosimplicial_object.δ_comp_σ_succ'_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {j : fin (n + 2)} {i : fin (n + 1)} (H : j = i.succ) {X' : C} (f' : X.obj (simplex_category.mk n) ⟶ X') :
X.δ j ≫ X.σ i ≫ f' = f'

The fourth cosimplicial identity

theorem category_theory.cosimplicial_object.δ_comp_σ_of_gt_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i : fin (n + 2)} {j : fin (n + 1)} (H : ⇑fin.cast_succ j < i) {X' : C} (f' : X.obj (simplex_category.mk (n + 1)) ⟶ X') :
X.δ i.succ ≫ X.σ (⇑fin.cast_succ j) ≫ f' = X.σ j ≫ X.δ i ≫ f'
theorem category_theory.cosimplicial_object.δ_comp_σ_of_gt'_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i : fin (n + 3)} {j : fin (n + 2)} (H : j.succ < i) {X' : C} (f' : X.obj (simplex_category.mk (n + 1)) ⟶ X') :
X.δ i ≫ X.σ j ≫ f' = X.σ (j.cast_lt _) ≫ X.δ (i.pred _) ≫ f'
theorem category_theory.cosimplicial_object.δ_comp_σ_of_gt' {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i : fin (n + 3)} {j : fin (n + 2)} (H : j.succ < i) :
X.δ i ≫ X.σ j = X.σ (j.cast_lt _) ≫ X.δ (i.pred _)
theorem category_theory.cosimplicial_object.σ_comp_σ_assoc {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) {n : ℕ} {i j : fin (n + 1)} (H : i ≤ j) {X' : C} (f' : X.obj (simplex_category.mk n) ⟶ X') :
X.σ (⇑fin.cast_succ i) ≫ X.σ j ≫ f' = X.σ j.succ ≫ X.σ i ≫ f'

The fifth cosimplicial identity

@[simp]
theorem category_theory.cosimplicial_object.δ_naturality_assoc {C : Type u} [category_theory.category C] {X' X : category_theory.cosimplicial_object C} (f : X ⟶ X') {n : ℕ} (i : fin (n + 2)) {X'_1 : C} (f' : X'.obj (simplex_category.mk (n + 1)) ⟶ X'_1) :
X.δ i ≫ f.app (simplex_category.mk (n + 1)) ≫ f' = f.app (simplex_category.mk n) ≫ X'.δ i ≫ f'
@[simp]
theorem category_theory.cosimplicial_object.σ_naturality_assoc {C : Type u} [category_theory.category C] {X' X : category_theory.cosimplicial_object C} (f : X ⟶ X') {n : ℕ} (i : fin (n + 1)) {X'_1 : C} (f' : X'.obj (simplex_category.mk n) ⟶ X'_1) :
X.σ i ≫ f.app (simplex_category.mk n) ≫ f' = f.app (simplex_category.mk (n + 1)) ≫ X'.σ i ≫ f'
@[reducible]

The constant cosimplicial object.

Augment a cosimplicial object with an object.

Equations
@[simp]
theorem category_theory.cosimplicial_object.augment_hom_app {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) (X₀ : C) (f : X₀ ⟶ X.obj (simplex_category.mk 0)) (w : ∀ (i : simplex_category) (g₁ g₂ : simplex_category.mk 0 ⟶ i), f ≫ X.map g₁ = f ≫ X.map g₂) (i : simplex_category) :
(X.augment X₀ f w).hom.app i = f ≫ X.map (i.const 0)
@[simp]
theorem category_theory.cosimplicial_object.augment_right {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) (X₀ : C) (f : X₀ ⟶ X.obj (simplex_category.mk 0)) (w : ∀ (i : simplex_category) (g₁ g₂ : simplex_category.mk 0 ⟶ i), f ≫ X.map g₁ = f ≫ X.map g₂) :
(X.augment X₀ f w).right = X
@[simp]
theorem category_theory.cosimplicial_object.augment_left {C : Type u} [category_theory.category C] (X : category_theory.cosimplicial_object C) (X₀ : C) (f : X₀ ⟶ X.obj (simplex_category.mk 0)) (w : ∀ (i : simplex_category) (g₁ g₂ : simplex_category.mk 0 ⟶ i), f ≫ X.map g₁ = f ≫ X.map g₂) :
(X.augment X₀ f w).left = X₀
@[simp]

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

Equations