Module: Mathlib.CategoryTheory.Sites.DenseSubsite.OneHypercoverDense

Goal state before:
pp: C₀ : Type u₀
C : Type u
inst✝² : Category.{v₀, u₀} C₀
inst✝¹ : Category.{v, u} C
F : C₀ ⥤ C
J₀ : GrothendieckTopology C₀
J : GrothendieckTopology C
inst✝ : IsDenseSubsite J₀ J F
X : C
data : F.OneHypercoverDenseData J₀ J X
i₁ i₂ : data.I₀
W : C
p₁ : W ⟶ F.obj (data.X i₁)
p₂ : W ⟶ F.obj (data.X i₂)
w : p₁ ≫ data.f i₁ = p₂ ≫ data.f i₂
this : F.IsCoverDense J
S : Sieve W :=
  Sieve.bind (Sieve.coverByImage F W).arrows fun Y f hf ↦
    Sieve.pullback (Nonempty.some hf).lift
      (Sieve.functorPushforward F
        (F.imageSieve ((Nonempty.some hf).map ≫ p₁) ⊓ F.imageSieve ((Nonempty.some hf).map ≫ p₂)))
T : Sieve W :=
  Sieve.bind S.arrows fun Z g hg ↦
    Sieve.pullback (Presieve.getFunctorPushforwardStructure ⋯).lift
      (Sieve.functorPushforward F (data.sieve₁₀ (Exists.choose ⋯) (Exists.choose ⋯)))
hS : S ∈ J W
hT : T ∈ J W
U V : C
a : U ⟶ V
b : V ⟶ W
hb : S.arrows b
str : Presieve.FunctorPushforwardStructure F
  (F.imageSieve ((Nonempty.some ⋯).map ≫ p₁) ⊓ F.imageSieve ((Nonempty.some ⋯).map ≫ p₂)).arrows
  ((Presieve.bind.bindStruct hb).g ≫ (Nonempty.some ⋯).lift) :=
  Presieve.getFunctorPushforwardStructure ⋯
W₀ : C₀
c : W₀ ⟶ (Presieve.getFunctorPushforwardStructure ⋯).preobj
d : U ⟶ F.obj W₀
fac : a ≫ (Presieve.getFunctorPushforwardStructure ⋯).lift = d ≫ F.map c
j : data.I₁ i₁ i₂
e : W₀ ⟶ data.Y j
h₁ : c ≫ Exists.choose ⋯ = e ≫ data.p₁ j
h₂ : c ≫ Exists.choose ⋯ = e ≫ data.p₂ j
⊢ ∃ j h, (a ≫ b) ≫ p₁ = h ≫ F.map (data.p₁ j) ∧ (a ≫ b) ≫ p₂ = h ≫ F.map (data.p₂ j)

Tactic:
refine ⟨j, d ≫ F.map e, ?_, ?_⟩

Goal state after:
case refine_1
C₀ : Type u₀
C : Type u
inst✝² : Category.{v₀, u₀} C₀
inst✝¹ : Category.{v, u} C
F : C₀ ⥤ C
J₀ : GrothendieckTopology C₀
J : GrothendieckTopology C
inst✝ : IsDenseSubsite J₀ J F
X : C
data : F.OneHypercoverDenseData J₀ J X
i₁ i₂ : data.I₀
W : C
p₁ : W ⟶ F.obj (data.X i₁)
p₂ : W ⟶ F.obj (data.X i₂)
w : p₁ ≫ data.f i₁ = p₂ ≫ data.f i₂
this : F.IsCoverDense J
S : Sieve W :=
  Sieve.bind (Sieve.coverByImage F W).arrows fun Y f hf ↦
    Sieve.pullback (Nonempty.some hf).lift
      (Sieve.functorPushforward F
        (F.imageSieve ((Nonempty.some hf).map ≫ p₁) ⊓ F.imageSieve ((Nonempty.some hf).map ≫ p₂)))
T : Sieve W :=
  Sieve.bind S.arrows fun Z g hg ↦
    Sieve.pullback (Presieve.getFunctorPushforwardStructure ⋯).lift
      (Sieve.functorPushforward F (data.sieve₁₀ (Exists.choose ⋯) (Exists.choose ⋯)))
hS : S ∈ J W
hT : T ∈ J W
U V : C
a : U ⟶ V
b : V ⟶ W
hb : S.arrows b
str : Presieve.FunctorPushforwardStructure F
  (F.imageSieve ((Nonempty.some ⋯).map ≫ p₁) ⊓ F.imageSieve ((Nonempty.some ⋯).map ≫ p₂)).arrows
  ((Presieve.bind.bindStruct hb).g ≫ (Nonempty.some ⋯).lift) :=
  Presieve.getFunctorPushforwardStructure ⋯
W₀ : C₀
c : W₀ ⟶ (Presieve.getFunctorPushforwardStructure ⋯).preobj
d : U ⟶ F.obj W₀
fac : a ≫ (Presieve.getFunctorPushforwardStructure ⋯).lift = d ≫ F.map c
j : data.I₁ i₁ i₂
e : W₀ ⟶ data.Y j
h₁ : c ≫ Exists.choose ⋯ = e ≫ data.p₁ j
h₂ : c ≫ Exists.choose ⋯ = e ≫ data.p₂ j
⊢ (a ≫ b) ≫ p₁ = (d ≫ F.map e) ≫ F.map (data.p₁ j)

case refine_2
C₀ : Type u₀
C : Type u
inst✝² : Category.{v₀, u₀} C₀
inst✝¹ : Category.{v, u} C
F : C₀ ⥤ C
J₀ : GrothendieckTopology C₀
J : GrothendieckTopology C
inst✝ : IsDenseSubsite J₀ J F
X : C
data : F.OneHypercoverDenseData J₀ J X
i₁ i₂ : data.I₀
W : C
p₁ : W ⟶ F.obj (data.X i₁)
p₂ : W ⟶ F.obj (data.X i₂)
w : p₁ ≫ data.f i₁ = p₂ ≫ data.f i₂
this : F.IsCoverDense J
S : Sieve W :=
  Sieve.bind (Sieve.coverByImage F W).arrows fun Y f hf ↦
    Sieve.pullback (Nonempty.some hf).lift
      (Sieve.functorPushforward F
        (F.imageSieve ((Nonempty.some hf).map ≫ p₁) ⊓ F.imageSieve ((Nonempty.some hf).map ≫ p₂)))
T : Sieve W :=
  Sieve.bind S.arrows fun Z g hg ↦
    Sieve.pullback (Presieve.getFunctorPushforwardStructure ⋯).lift
      (Sieve.functorPushforward F (data.sieve₁₀ (Exists.choose ⋯) (Exists.choose ⋯)))
hS : S ∈ J W
hT : T ∈ J W
U V : C
a : U ⟶ V
b : V ⟶ W
hb : S.arrows b
str : Presieve.FunctorPushforwardStructure F
  (F.imageSieve ((Nonempty.some ⋯).map ≫ p₁) ⊓ F.imageSieve ((Nonempty.some ⋯).map ≫ p₂)).arrows
  ((Presieve.bind.bindStruct hb).g ≫ (Nonempty.some ⋯).lift) :=
  Presieve.getFunctorPushforwardStructure ⋯
W₀ : C₀
c : W₀ ⟶ (Presieve.getFunctorPushforwardStructure ⋯).preobj
d : U ⟶ F.obj W₀
fac : a ≫ (Presieve.getFunctorPushforwardStructure ⋯).lift = d ≫ F.map c
j : data.I₁ i₁ i₂
e : W₀ ⟶ data.Y j
h₁ : c ≫ Exists.choose ⋯ = e ≫ data.p₁ j
h₂ : c ≫ Exists.choose ⋯ = e ≫ data.p₂ j
⊢ (a ≫ b) ≫ p₂ = (d ≫ F.map e) ≫ F.map (data.p₂ j)