-- Mathlib/AlgebraicTopology/DoldKan/FunctorGamma.lean
theorem map_on_summand₀ {Δ Δ' : SimplexCategoryᵒᵖ} (A : Splitting.IndexSet Δ) {θ : Δ ⟶ Δ'}
    {Δ'' : SimplexCategory} {e : Δ'.unop ⟶ Δ''} {i : Δ'' ⟶ A.1.unop} [Epi e] [Mono i]
    (fac : e ≫ i = θ.unop ≫ A.e) :
    Sigma.ι (summand K Δ) A ≫ map K θ =
      Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)

Proof state:
case e_a.e_i
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ image.ι (θ.unop ≫ A.e) = i

Tactic:
exact SimplexCategory.image_ι_eq fac

Result:
no goals

Proof state:
case e_a.h.e_6.h.e_f
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ factorThruImage (θ.unop ≫ A.e) = e

Tactic:
exact SimplexCategory.factorThruImage_eq fac

Result:
no goals

Proof state:
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
Δ'' : SimplexCategory
e : unop Δ' ⟶ Δ''
i : Δ'' ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ Sigma.ι (summand K Δ) A ≫ map K θ = Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)

Tactic:
simp only [map, colimit.ι_desc, Cofan.mk_ι_app]

Result:
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
Δ'' : SimplexCategory
e : unop Δ' ⟶ Δ''
i : Δ'' ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ Termwise.mapMono K (image.ι (θ.unop ≫ A.e)) ≫ Sigma.ι (summand K Δ') (A.pull θ) =
    Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)

Proof state:
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
Δ'' : SimplexCategory
e : unop Δ' ⟶ Δ''
i : Δ'' ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
h : image (θ.unop ≫ A.e) = Δ''
⊢ Termwise.mapMono K (image.ι (θ.unop ≫ A.e)) ≫ Sigma.ι (summand K Δ') (A.pull θ) =
    Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)

Tactic:
subst h

Result:
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ Termwise.mapMono K (image.ι (θ.unop ≫ A.e)) ≫ Sigma.ι (summand K Δ') (A.pull θ) =
    Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)

Proof state:
case e_a.h.e_6.h
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ Splitting.IndexSet.mk (factorThruImage (θ.unop ≫ A.e)) = Splitting.IndexSet.mk e

Tactic:
congr

Result:
case e_a.h.e_6.h.e_f
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ factorThruImage (θ.unop ≫ A.e) = e

Proof state:
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ Termwise.mapMono K (image.ι (θ.unop ≫ A.e)) ≫ Sigma.ι (summand K Δ') (A.pull θ) =
    Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)

Tactic:
congr

Result:
case e_a.e_i
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ image.ι (θ.unop ≫ A.e) = i

case e_a.h.e_6.h
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ A.pull θ = Splitting.IndexSet.mk e

Proof state:
case e_a.h.e_6.h
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ A.pull θ = Splitting.IndexSet.mk e

Tactic:
dsimp only [SimplicialObject.Splitting.IndexSet.pull]

Result:
case e_a.h.e_6.h
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
e : unop Δ' ⟶ image (θ.unop ≫ A.e)
i : image (θ.unop ≫ A.e) ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ Splitting.IndexSet.mk (factorThruImage (θ.unop ≫ A.e)) = Splitting.IndexSet.mk e

Proof state:
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
Δ'' : SimplexCategory
e : unop Δ' ⟶ Δ''
i : Δ'' ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
⊢ Termwise.mapMono K (image.ι (θ.unop ≫ A.e)) ≫ Sigma.ι (summand K Δ') (A.pull θ) =
    Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)

Tactic:
have h := SimplexCategory.image_eq fac

Result:
C : Type u_1
inst✝⁴ : Category.{u_2, u_1} C
inst✝³ : Preadditive C
K : ChainComplex C ℕ
inst✝² : HasFiniteCoproducts C
Δ Δ' : SimplexCategoryᵒᵖ
A : Splitting.IndexSet Δ
θ : Δ ⟶ Δ'
Δ'' : SimplexCategory
e : unop Δ' ⟶ Δ''
i : Δ'' ⟶ unop A.fst
inst✝¹ : Epi e
inst✝ : Mono i
fac : e ≫ i = θ.unop ≫ A.e
h : image (θ.unop ≫ A.e) = Δ''
⊢ Termwise.mapMono K (image.ι (θ.unop ≫ A.e)) ≫ Sigma.ι (summand K Δ') (A.pull θ) =
    Termwise.mapMono K i ≫ Sigma.ι (summand K Δ') (Splitting.IndexSet.mk e)