# Exact sequences #

A sequence of n composable arrows S : ComposableArrows C (i.e. a functor S : Fin (n + 1) ⥤ C) is said to be exact (S.Exact) if the composition of two consecutive arrows are zero (S.IsComplex) and the diagram is exact at each i for 1 ≤ i < n.

Together with the inductive construction of composable arrows ComposableArrows.precomp, this is useful in order to state that certain finite sequences of morphisms are exact (e.g the snake lemma), even though in the applications it would usually be more convenient to use individual lemmas expressing the exactness at a particular object.

This implementation is a refactor of exact_seq with appeared in the Liquid Tensor Experiment as a property of lists in Arrow C.

@[simp]
theorem CategoryTheory.ShortComplex.toComposableArrows_map {C : Type u_1} [] (S : ) :
∀ {X Y : Fin (1 + 1 + 1)} (g : X Y), S.toComposableArrows.map g =
@[simp]
theorem CategoryTheory.ShortComplex.toComposableArrows_obj {C : Type u_1} [] (S : ) :
∀ (a : Fin (1 + 1 + 1)), S.toComposableArrows.obj a =

The composable arrows associated to a short complex.

Equations
• S.toComposableArrows =
Instances For
structure CategoryTheory.ComposableArrows.IsComplex {C : Type u_1} [] {n : } (S : ) :

F : ComposableArrows C n is a complex if all compositions of two consecutive arrows are zero.

Instances For
theorem CategoryTheory.ComposableArrows.IsComplex.zero {C : Type u_1} [] {n : } {S : } (self : S.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
CategoryTheory.CategoryStruct.comp (S.map' i (i + 1) ) (S.map' (i + 1) (i + 2) hi) = 0

the composition of two consecutive arrows is zero

theorem CategoryTheory.ComposableArrows.IsComplex.zero_assoc {C : Type u_1} [] {n : } {S : } (self : S.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) {Z : C} (h : S.obj i + 2, Z) :
CategoryTheory.CategoryStruct.comp (S.map' i (i + 1) ) (CategoryTheory.CategoryStruct.comp (S.map' (i + 1) (i + 2) hi) h) =
theorem CategoryTheory.ComposableArrows.IsComplex.zero'_assoc {C : Type u_1} [] {n : } {S : } (hS : S.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) {Z : C} (h : S.obj k, Z) :
CategoryTheory.CategoryStruct.comp (S.map' i j ) (CategoryTheory.CategoryStruct.comp (S.map' j k hk) h) =
theorem CategoryTheory.ComposableArrows.IsComplex.zero' {C : Type u_1} [] {n : } {S : } (hS : S.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
CategoryTheory.CategoryStruct.comp (S.map' i j ) (S.map' j k hk) = 0
theorem CategoryTheory.ComposableArrows.isComplex_of_iso {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.IsComplex) :
S₂.IsComplex
theorem CategoryTheory.ComposableArrows.isComplex_iff_of_iso {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) :
S₁.IsComplex S₂.IsComplex
theorem CategoryTheory.ComposableArrows.isComplex₀ {C : Type u_1} [] (S : ) :
S.IsComplex
theorem CategoryTheory.ComposableArrows.isComplex₁ {C : Type u_1} [] (S : ) :
S.IsComplex
@[reducible, inline]
abbrev CategoryTheory.ComposableArrows.sc' {C : Type u_1} [] {n : } (S : ) (hS : S.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :

The short complex consisting of maps S.map' i j and S.map' j k when we know that S : ComposableArrows C n satisfies S.IsComplex.

Equations
Instances For
@[reducible, inline]
abbrev CategoryTheory.ComposableArrows.sc {C : Type u_1} [] {n : } (S : ) (hS : S.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :

The short complex consisting of maps S.map' i (i + 1) and S.map' (i + 1) (i + 2) when we know that S : ComposableArrows C n satisfies S.IsComplex.

Equations
• S.sc hS i hi = S.sc' hS i (i + 1) (i + 2)
Instances For
structure CategoryTheory.ComposableArrows.Exact {C : Type u_1} [] {n : } (S : ) extends :

F : ComposableArrows C n is exact if it is a complex and that all short complexes consisting of two consecutive arrows are exact.

Instances For
theorem CategoryTheory.ComposableArrows.Exact.exact {C : Type u_1} [] {n : } {S : } (self : S.Exact) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
(S.sc i ).Exact
theorem CategoryTheory.ComposableArrows.Exact.exact' {C : Type u_1} [] {n : } {S : } (hS : S.Exact) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
(S.sc' i j k ).Exact
@[simp]
theorem CategoryTheory.ComposableArrows.sc'Map_τ₂ {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
(CategoryTheory.ComposableArrows.sc'Map φ h₁ h₂ i j k hij hjk hk).τ₂ = φ.app j,
@[simp]
theorem CategoryTheory.ComposableArrows.sc'Map_τ₃ {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
(CategoryTheory.ComposableArrows.sc'Map φ h₁ h₂ i j k hij hjk hk).τ₃ = φ.app k,
@[simp]
theorem CategoryTheory.ComposableArrows.sc'Map_τ₁ {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
(CategoryTheory.ComposableArrows.sc'Map φ h₁ h₂ i j k hij hjk hk).τ₁ = φ.app i,
def CategoryTheory.ComposableArrows.sc'Map {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
S₁.sc' h₁ i j k S₂.sc' h₂ i j k

Functoriality maps for ComposableArrows.sc'.

Equations
• CategoryTheory.ComposableArrows.sc'Map φ h₁ h₂ i j k hij hjk hk = { τ₁ := φ.app i, , τ₂ := φ.app j, , τ₃ := φ.app k, , comm₁₂ := , comm₂₃ := }
Instances For
@[simp]
theorem CategoryTheory.ComposableArrows.scMap_τ₃ {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
(CategoryTheory.ComposableArrows.scMap φ h₁ h₂ i hi).τ₃ = φ.app i + 2,
@[simp]
theorem CategoryTheory.ComposableArrows.scMap_τ₂ {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
(CategoryTheory.ComposableArrows.scMap φ h₁ h₂ i hi).τ₂ = φ.app i + 1,
@[simp]
theorem CategoryTheory.ComposableArrows.scMap_τ₁ {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
(CategoryTheory.ComposableArrows.scMap φ h₁ h₂ i hi).τ₁ = φ.app i,
def CategoryTheory.ComposableArrows.scMap {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (φ : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
S₁.sc h₁ i S₂.sc h₂ i

Functoriality maps for ComposableArrows.sc.

Equations
Instances For
@[simp]
theorem CategoryTheory.ComposableArrows.sc'MapIso_hom {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
(CategoryTheory.ComposableArrows.sc'MapIso e h₁ h₂ i j k hij hjk hk).hom = CategoryTheory.ComposableArrows.sc'Map e.hom h₁ h₂ i j k
@[simp]
theorem CategoryTheory.ComposableArrows.sc'MapIso_inv {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
(CategoryTheory.ComposableArrows.sc'MapIso e h₁ h₂ i j k hij hjk hk).inv = CategoryTheory.ComposableArrows.sc'Map e.inv h₂ h₁ i j k
def CategoryTheory.ComposableArrows.sc'MapIso {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (j : ) (k : ) (hij : autoParam (i + 1 = j) _auto✝) (hjk : autoParam (j + 1 = k) _auto✝) (hk : autoParam (k n) _auto✝) :
S₁.sc' h₁ i j k S₂.sc' h₂ i j k

The isomorphism S₁.sc' _ i j k ≅ S₂.sc' _ i j k induced by an isomorphism S₁ ≅ S₂ in ComposableArrows C n.

Equations
• One or more equations did not get rendered due to their size.
Instances For
@[simp]
theorem CategoryTheory.ComposableArrows.scMapIso_inv {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
@[simp]
theorem CategoryTheory.ComposableArrows.scMapIso_hom {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
def CategoryTheory.ComposableArrows.scMapIso {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.IsComplex) (h₂ : S₂.IsComplex) (i : ) (hi : autoParam (i + 2 n) _auto✝) :
S₁.sc h₁ i S₂.sc h₂ i

The isomorphism S₁.sc _ i ≅ S₂.sc _ i induced by an isomorphism S₁ ≅ S₂ in ComposableArrows C n.

Equations
• One or more equations did not get rendered due to their size.
Instances For
theorem CategoryTheory.ComposableArrows.exact_of_iso {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) (h₁ : S₁.Exact) :
S₂.Exact
theorem CategoryTheory.ComposableArrows.exact_iff_of_iso {C : Type u_1} [] {n : } {S₁ : } {S₂ : } (e : S₁ S₂) :
S₁.Exact S₂.Exact
theorem CategoryTheory.ComposableArrows.exact₀ {C : Type u_1} [] (S : ) :
S.Exact
theorem CategoryTheory.ComposableArrows.exact₁ {C : Type u_1} [] (S : ) :
S.Exact
theorem CategoryTheory.ComposableArrows.isComplex₂_iff {C : Type u_1} [] (S : ) :
S.IsComplex CategoryTheory.CategoryStruct.comp (S.map' 0 1 ) (S.map' 1 2 ) = 0
theorem CategoryTheory.ComposableArrows.isComplex₂_mk {C : Type u_1} [] (S : ) (w : CategoryTheory.CategoryStruct.comp (S.map' 0 1 ) (S.map' 1 2 ) = 0) :
S.IsComplex
theorem CategoryTheory.ShortComplex.isComplex_toComposableArrows {C : Type u_1} [] (S : ) :
S.toComposableArrows.IsComplex
theorem CategoryTheory.ComposableArrows.exact₂_iff {C : Type u_1} [] (S : ) (hS : S.IsComplex) :
S.Exact (S.sc' hS 0 1 2 ).Exact
theorem CategoryTheory.ComposableArrows.exact₂_mk {C : Type u_1} [] (S : ) (w : CategoryTheory.CategoryStruct.comp (S.map' 0 1 ) (S.map' 1 2 ) = 0) (h : (CategoryTheory.ShortComplex.mk (S.map' 0 1 ) (S.map' 1 2 ) w).Exact) :
S.Exact
theorem CategoryTheory.ShortComplex.Exact.exact_toComposableArrows {C : Type u_1} [] {S : } (hS : S.Exact) :
S.toComposableArrows.Exact
theorem CategoryTheory.ShortComplex.exact_iff_exact_toComposableArrows {C : Type u_1} [] (S : ) :
S.Exact S.toComposableArrows.Exact
theorem CategoryTheory.ComposableArrows.exact_iff_δ₀ {C : Type u_1} [] {n : } (S : ) :
S.Exact (CategoryTheory.ComposableArrows.mk₂ (S.map' 0 1 ) (S.map' 1 2 )).Exact S.δ₀.Exact
theorem CategoryTheory.ComposableArrows.Exact.δ₀ {C : Type u_1} [] {n : } {S : } (hS : S.Exact) :
S.δ₀.Exact
theorem CategoryTheory.ComposableArrows.exact_of_δ₀ {C : Type u_1} [] {n : } {S : } (h : (CategoryTheory.ComposableArrows.mk₂ (S.map' 0 1 ) (S.map' 1 2 )).Exact) (h₀ : S.δ₀.Exact) :
S.Exact

If S : ComposableArrows C (n + 2) is such that the first two arrows form an exact sequence and that the tail S.δ₀ is exact, then S is also exact. See ShortComplex.SnakeInput.snake_lemma in Algebra.Homology.ShortComplex.SnakeLemma for a use of this lemma.

theorem CategoryTheory.ComposableArrows.exact_iff_δlast {C : Type u_1} [] {n : } (S : ) :
S.Exact S.δlast.Exact (CategoryTheory.ComposableArrows.mk₂ (S.map' n (n + 1) ) (S.map' (n + 1) (n + 2) )).Exact
theorem CategoryTheory.ComposableArrows.Exact.δlast {C : Type u_1} [] {n : } {S : } (hS : S.Exact) :
S.δlast.Exact
theorem CategoryTheory.ComposableArrows.exact_of_δlast {C : Type u_1} [] {n : } (S : ) (h₁ : S.δlast.Exact) (h₂ : (CategoryTheory.ComposableArrows.mk₂ (S.map' n (n + 1) ) (S.map' (n + 1) (n + 2) )).Exact) :
S.Exact