Module: Mathlib.CategoryTheory.Sites.Hypercover.One

Goal state before:
pp: case refine_1.refine_2
C : Type u
inst✝¹ : Category.{v, u} C
S : C
E : PreOneHypercover S
F : PreOneHypercover S
inst✝ : HasPullbacks C
i j : E.I₀ × F.I₀
W : C
p₁ : W ⟶ pullback (E.f i.1) (F.f i.2)
p₂ : W ⟶ pullback (E.f j.1) (F.f j.2)
w : p₁ ≫ pullback.fst (E.f i.1) (F.f i.2) ≫ E.f i.1 = p₂ ≫ pullback.fst (E.f j.1) (F.f j.2) ≫ E.f j.1
Y : C
f : Y ⟶ W
p : W ⟶ pullback ((E.inter F).f i) ((E.inter F).f j) := pullback.lift p₁ p₂ w
x✝ : ((E.inter F).sieve₁ p₁ p₂).arrows f
k : (E.inter F).I₁ i j
a : Y ⟶ (E.inter F).Y k
h₁ : f ≫ p₁ = a ≫ (E.inter F).p₁ k
h₂ : f ≫ p₂ = a ≫ (E.inter F).p₂ k
⊢ (E.sieve₁ (p₁ ≫ pullback.fst (E.f i.1) (F.f i.2)) (p₂ ≫ pullback.fst (E.f j.1) (F.f j.2))).arrows
    (pullback.fst p ((E.inter F).toPullback k))

pp: case refine_1.refine_3
C : Type u
inst✝¹ : Category.{v, u} C
S : C
E : PreOneHypercover S
F : PreOneHypercover S
inst✝ : HasPullbacks C
i j : E.I₀ × F.I₀
W : C
p₁ : W ⟶ pullback (E.f i.1) (F.f i.2)
p₂ : W ⟶ pullback (E.f j.1) (F.f j.2)
w : p₁ ≫ pullback.fst (E.f i.1) (F.f i.2) ≫ E.f i.1 = p₂ ≫ pullback.fst (E.f j.1) (F.f j.2) ≫ E.f j.1
Y : C
f : Y ⟶ W
p : W ⟶ pullback ((E.inter F).f i) ((E.inter F).f j) := pullback.lift p₁ p₂ w
x✝ : ((E.inter F).sieve₁ p₁ p₂).arrows f
k : (E.inter F).I₁ i j
a : Y ⟶ (E.inter F).Y k
h₁ : f ≫ p₁ = a ≫ (E.inter F).p₁ k
h₂ : f ≫ p₂ = a ≫ (E.inter F).p₂ k
⊢ (fun x x_1 h ↦
      ((fun x f x_2 ↦
            Sieve.pullback f (F.sieve₁ (p₁ ≫ pullback.snd (E.f i.1) (F.f i.2)) (p₂ ≫ pullback.snd (E.f j.1) (F.f j.2))))
          x x_1 h).arrows)
    (pullback p ((E.inter F).toPullback k)) (pullback.fst p ((E.inter F).toPullback k)) ?refine_1.refine_2
    (pullback.lift f a ⋯)

pp: case refine_1.refine_4
C : Type u
inst✝¹ : Category.{v, u} C
S : C
E : PreOneHypercover S
F : PreOneHypercover S
inst✝ : HasPullbacks C
i j : E.I₀ × F.I₀
W : C
p₁ : W ⟶ pullback (E.f i.1) (F.f i.2)
p₂ : W ⟶ pullback (E.f j.1) (F.f j.2)
w : p₁ ≫ pullback.fst (E.f i.1) (F.f i.2) ≫ E.f i.1 = p₂ ≫ pullback.fst (E.f j.1) (F.f j.2) ≫ E.f j.1
Y : C
f : Y ⟶ W
p : W ⟶ pullback ((E.inter F).f i) ((E.inter F).f j) := pullback.lift p₁ p₂ w
x✝ : ((E.inter F).sieve₁ p₁ p₂).arrows f
k : (E.inter F).I₁ i j
a : Y ⟶ (E.inter F).Y k
h₁ : f ≫ p₁ = a ≫ (E.inter F).p₁ k
h₂ : f ≫ p₂ = a ≫ (E.inter F).p₂ k
⊢ pullback.lift f a ⋯ ≫ pullback.fst p ((E.inter F).toPullback k) = f

Tactic:
· refine ⟨k.1, pullback.snd _ _ ≫ pullback.fst _ _, ?_, ?_⟩
      · have : p₁ ≫ pullback.fst (E.f i.1) (F.f i.2) = p ≫ pullback.fst _ _ ≫ pullback.fst _ _ := by
          simp [p]
        simp [this, pullback.condition_assoc, toPullback]
      · have : p₂ ≫ pullback.fst (E.f j.1) (F.f j.2) = p ≫ pullback.snd _ _ ≫ pullback.fst _ _ := by
          simp [p]
        simp [this, pullback.condition_assoc, toPullback]

Goal state after:
case refine_1.refine_3
C : Type u
inst✝¹ : Category.{v, u} C
S : C
E : PreOneHypercover S
F : PreOneHypercover S
inst✝ : HasPullbacks C
i j : E.I₀ × F.I₀
W : C
p₁ : W ⟶ pullback (E.f i.1) (F.f i.2)
p₂ : W ⟶ pullback (E.f j.1) (F.f j.2)
w : p₁ ≫ pullback.fst (E.f i.1) (F.f i.2) ≫ E.f i.1 = p₂ ≫ pullback.fst (E.f j.1) (F.f j.2) ≫ E.f j.1
Y : C
f : Y ⟶ W
p : W ⟶ pullback ((E.inter F).f i) ((E.inter F).f j) := pullback.lift p₁ p₂ w
x✝ : ((E.inter F).sieve₁ p₁ p₂).arrows f
k : (E.inter F).I₁ i j
a : Y ⟶ (E.inter F).Y k
h₁ : f ≫ p₁ = a ≫ (E.inter F).p₁ k
h₂ : f ≫ p₂ = a ≫ (E.inter F).p₂ k
⊢ (fun x x_1 h ↦
      ((fun x f x_2 ↦
            Sieve.pullback f (F.sieve₁ (p₁ ≫ pullback.snd (E.f i.1) (F.f i.2)) (p₂ ≫ pullback.snd (E.f j.1) (F.f j.2))))
          x x_1 h).arrows)
    (pullback p ((E.inter F).toPullback k)) (pullback.fst p ((E.inter F).toPullback k)) ⋯ (pullback.lift f a ⋯)

case refine_1.refine_4
C : Type u
inst✝¹ : Category.{v, u} C
S : C
E : PreOneHypercover S
F : PreOneHypercover S
inst✝ : HasPullbacks C
i j : E.I₀ × F.I₀
W : C
p₁ : W ⟶ pullback (E.f i.1) (F.f i.2)
p₂ : W ⟶ pullback (E.f j.1) (F.f j.2)
w : p₁ ≫ pullback.fst (E.f i.1) (F.f i.2) ≫ E.f i.1 = p₂ ≫ pullback.fst (E.f j.1) (F.f j.2) ≫ E.f j.1
Y : C
f : Y ⟶ W
p : W ⟶ pullback ((E.inter F).f i) ((E.inter F).f j) := pullback.lift p₁ p₂ w
x✝ : ((E.inter F).sieve₁ p₁ p₂).arrows f
k : (E.inter F).I₁ i j
a : Y ⟶ (E.inter F).Y k
h₁ : f ≫ p₁ = a ≫ (E.inter F).p₁ k
h₂ : f ≫ p₂ = a ≫ (E.inter F).p₂ k
⊢ pullback.lift f a ⋯ ≫ pullback.fst p ((E.inter F).toPullback k) = f