-- Mathlib/CategoryTheory/Sites/CoverPreserving.lean
theorem compatiblePreservingOfFlat {C : Type u₁} [Category.{v₁} C] {D : Type u₁} [Category.{v₁} D]
    (K : GrothendieckTopology D) (G : C ⥤ D) [RepresentablyFlat G] : CompatiblePreserving K G

Proof state:
case compatible
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
eq₂ : f₂ = (c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯
⊢ ℱ.val.map ((c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯).op (x g₁ hg₁) = ℱ.val.map f₂.op (x g₂ hg₂)

Tactic:
conv_rhs => rw [eq₂]

Result:
case compatible
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
eq₂ : f₂ = (c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯
⊢ ℱ.val.map ((c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯).op (x g₁ hg₁) =
    ℱ.val.map ((c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯).op (x g₂ hg₂)

Proof state:
case compatible
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
eq₂ : f₂ = (c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯
⊢ ℱ.val.map ((c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯).op (x g₁ hg₁) =
    ℱ.val.map ((c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯).op (x g₂ hg₂)

Tactic:
simp only [c, op_comp, Functor.map_comp, types_comp_apply, eqToHom_op, eqToHom_map]

Result:
case compatible
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
eq₂ : f₂ = (c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯
⊢ ℱ.val.map c'.pt.hom.op (ℱ.val.map (G.map (c'.π.app left).right).op (eqToHom ⋯ (x g₁ hg₁))) =
    ℱ.val.map c'.pt.hom.op (ℱ.val.map (G.map (c'.π.app right).right).op (eqToHom ⋯ (x g₂ hg₂)))

Proof state:
case compatible
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
⊢ ℱ.val.map f₁.op (x g₁ hg₁) = ℱ.val.map f₂.op (x g₂ hg₂)

Tactic:
have eq₂ : f₂ = (c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom (by simp) := by
  erw [← (c'.π.app right).w]
  dsimp [c]
  simp

Result:
case compatible
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
eq₂ : f₂ = (c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯
⊢ ℱ.val.map f₁.op (x g₁ hg₁) = ℱ.val.map f₂.op (x g₂ hg₂)

Proof state:
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
⊢ f₂ = (c'.pt.hom ≫ G.map (c'.π.app right).right) ≫ eqToHom ⋯

Tactic:
erw [← (c'.π.app right).w]

Result:
C : Type u₁
inst✝² : Category.{v₁, u₁} C
D : Type u₁
inst✝¹ : Category.{v₁, u₁} D
K : GrothendieckTopology D
G : C ⥤ D
inst✝ : RepresentablyFlat G
ℱ : Sheaf K (Type u_1)
Z : C
T : Presieve Z
x : FamilyOfElements (G.op ⋙ ℱ.val) T
hx : x.Compatible
Y₁ Y₂ : C
X : D
f₁ : X ⟶ G.obj Y₁
f₂ : X ⟶ G.obj Y₂
g₁ : Y₁ ⟶ Z
g₂ : Y₂ ⟶ Z
hg₁ : T g₁
hg₂ : T g₂
e : f₁ ≫ G.map g₁ = f₂ ≫ G.map g₂
c : Cone (cospan g₁ g₂ ⋙ G) :=
  (Cones.postcompose (diagramIsoCospan (cospan g₁ g₂ ⋙ G)).inv).obj (PullbackCone.mk f₁ f₂ e)
c' : Cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G) :=
  IsCofiltered.cone (c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G)
eq₁ : f₁ = (c'.pt.hom ≫ G.map (c'.π.app left).right) ≫ eqToHom ⋯
⊢ f₂ =
    ((Functor.fromPUnit c.pt).map (c'.π.app right).left ≫
        ((c.toStructuredArrow ⋙ StructuredArrow.pre c.pt (cospan g₁ g₂) G).obj right).hom) ≫
      eqToHom ⋯