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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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } {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 : } (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 : } (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