Module: Mathlib.CategoryTheory.Sites.Coherent.RegularSheaves

Goal state before:
pp: case refine_1
C : Type u_1
inst✝¹ : Category.{v_1, u_1} C
P : Cᵒᵖ ⥤ Type u_4
X B : C
π : X ⟶ B
inst✝ : EffectiveEpi π
c : PullbackCone π π
hc : IsLimit c
this : HasPullback π π
hP :
  ∀
    (b :
      (fun X ↦ X)
        ↑{x |
            (ConcreteCategory.hom (P.map (pullback.fst π π).op)) x =
              (ConcreteCategory.hom (P.map (pullback.snd π π).op)) x}),
    ∃! a, (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = b
b : P.obj (op X)
hb : (ConcreteCategory.hom (P.map c.fst.op)) b = (ConcreteCategory.hom (P.map c.snd.op)) b
h₁ : ((pullbackIsPullback π π).conePointUniqueUpToIso hc).hom ≫ c.fst = pullback.fst π π
hb' : (ConcreteCategory.hom (P.map (pullback.fst π π).op)) b = (ConcreteCategory.hom (P.map (pullback.snd π π).op)) b
a : P.obj (op B)
ha₁ : (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = ⟨b, hb'⟩
ha₂ :
  ∀ (y : (fun X ↦ X) (P.obj (op B))),
    (fun a ↦ (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = ⟨b, hb'⟩) y → y = a
⊢ (fun x ↦ (ConcreteCategory.hom (P.map π.op)) x = b) a

pp: case refine_2
C : Type u_1
inst✝¹ : Category.{v_1, u_1} C
P : Cᵒᵖ ⥤ Type u_4
X B : C
π : X ⟶ B
inst✝ : EffectiveEpi π
c : PullbackCone π π
hc : IsLimit c
this : HasPullback π π
hP :
  ∀
    (b :
      (fun X ↦ X)
        ↑{x |
            (ConcreteCategory.hom (P.map (pullback.fst π π).op)) x =
              (ConcreteCategory.hom (P.map (pullback.snd π π).op)) x}),
    ∃! a, (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = b
b : P.obj (op X)
hb : (ConcreteCategory.hom (P.map c.fst.op)) b = (ConcreteCategory.hom (P.map c.snd.op)) b
h₁ : ((pullbackIsPullback π π).conePointUniqueUpToIso hc).hom ≫ c.fst = pullback.fst π π
hb' : (ConcreteCategory.hom (P.map (pullback.fst π π).op)) b = (ConcreteCategory.hom (P.map (pullback.snd π π).op)) b
a : P.obj (op B)
ha₁ : (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = ⟨b, hb'⟩
ha₂ :
  ∀ (y : (fun X ↦ X) (P.obj (op B))),
    (fun a ↦ (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = ⟨b, hb'⟩) y → y = a
⊢ ∀ (y : P.obj (op B)), (fun x ↦ (ConcreteCategory.hom (P.map π.op)) x = b) y → y = a

Tactic:
· simpa [mapToEqualizer] using ha₁

Goal state after:
case refine_2
C : Type u_1
inst✝¹ : Category.{v_1, u_1} C
P : Cᵒᵖ ⥤ Type u_4
X B : C
π : X ⟶ B
inst✝ : EffectiveEpi π
c : PullbackCone π π
hc : IsLimit c
this : HasPullback π π
hP :
  ∀
    (b :
      (fun X ↦ X)
        ↑{x |
            (ConcreteCategory.hom (P.map (pullback.fst π π).op)) x =
              (ConcreteCategory.hom (P.map (pullback.snd π π).op)) x}),
    ∃! a, (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = b
b : P.obj (op X)
hb : (ConcreteCategory.hom (P.map c.fst.op)) b = (ConcreteCategory.hom (P.map c.snd.op)) b
h₁ : ((pullbackIsPullback π π).conePointUniqueUpToIso hc).hom ≫ c.fst = pullback.fst π π
hb' : (ConcreteCategory.hom (P.map (pullback.fst π π).op)) b = (ConcreteCategory.hom (P.map (pullback.snd π π).op)) b
a : P.obj (op B)
ha₁ : (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = ⟨b, hb'⟩
ha₂ :
  ∀ (y : (fun X ↦ X) (P.obj (op B))),
    (fun a ↦ (ConcreteCategory.hom (mapToEqualizer P π (pullback.fst π π) (pullback.snd π π) ⋯)) a = ⟨b, hb'⟩) y → y = a
⊢ ∀ (y : P.obj (op B)), (fun x ↦ (ConcreteCategory.hom (P.map π.op)) x = b) y → y = a