-- Mathlib/CategoryTheory/Functor/Flat.lean
theorem uniq {K : J ⥤ C} {c : Cone K} (hc : IsLimit c) (s : Cone (K ⋙ F))
    (f₁ f₂ : s.pt ⟶ F.obj c.pt) (h₁ : ∀ j : J, f₁ ≫ (F.mapCone c).π.app j = s.π.app j)
    (h₂ : ∀ j : J, f₂ ≫ (F.mapCone c).π.app j = s.π.app j) : f₁ = f₂

Proof state:
C : Type u₁
inst✝⁴ : Category.{v₁, u₁} C
D : Type u₂
inst✝³ : Category.{v₂, u₂} D
J : Type v₁
inst✝² : SmallCategory J
inst✝¹ : FinCategory J
F : C ⥤ D
inst✝ : RepresentablyFlat F
K : J ⥤ C
c : Cone K
hc : IsLimit c
s : Cone (K ⋙ F)
f₁ f₂ : s.pt ⟶ F.obj c.pt
h₁ : ∀ (j : J), f₁ ≫ (F.mapCone c).π.app j = s.π.app j
h₂ : ∀ (j : J), f₂ ≫ (F.mapCone c).π.app j = s.π.app j
α₁ : (F.mapCone c).toStructuredArrow ⋙ map f₁ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
α₂ : (F.mapCone c).toStructuredArrow ⋙ map f₂ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
c₁ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₁ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₁)
c₂ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₂ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₂)
c₀ : Cone (biconeMk J c₁ c₂) := IsCofiltered.cone (biconeMk J c₁ c₂)
g₁ : c₀.pt ⟶ c₁.pt := c₀.π.app Bicone.left
g₂ : c₀.pt ⟶ c₂.pt := c₀.π.app Bicone.right
this✝ : ∀ (j : J), g₁.right ≫ c.π.app j = g₂.right ≫ c.π.app j
this : c.extend g₁.right = c.extend g₂.right
⊢ g₁.right = hc.lift (c.extend g₁.right)

Tactic:
apply hc.uniq (c.extend _)

Result:
case x
C : Type u₁
inst✝⁴ : Category.{v₁, u₁} C
D : Type u₂
inst✝³ : Category.{v₂, u₂} D
J : Type v₁
inst✝² : SmallCategory J
inst✝¹ : FinCategory J
F : C ⥤ D
inst✝ : RepresentablyFlat F
K : J ⥤ C
c : Cone K
hc : IsLimit c
s : Cone (K ⋙ F)
f₁ f₂ : s.pt ⟶ F.obj c.pt
h₁ : ∀ (j : J), f₁ ≫ (F.mapCone c).π.app j = s.π.app j
h₂ : ∀ (j : J), f₂ ≫ (F.mapCone c).π.app j = s.π.app j
α₁ : (F.mapCone c).toStructuredArrow ⋙ map f₁ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
α₂ : (F.mapCone c).toStructuredArrow ⋙ map f₂ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
c₁ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₁ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₁)
c₂ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₂ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₂)
c₀ : Cone (biconeMk J c₁ c₂) := IsCofiltered.cone (biconeMk J c₁ c₂)
g₁ : c₀.pt ⟶ c₁.pt := c₀.π.app Bicone.left
g₂ : c₀.pt ⟶ c₂.pt := c₀.π.app Bicone.right
this✝ : ∀ (j : J), g₁.right ≫ c.π.app j = g₂.right ≫ c.π.app j
this : c.extend g₁.right = c.extend g₂.right
⊢ ∀ (j : J), g₁.right ≫ c.π.app j = (c.extend g₁.right).π.app j

Proof state:
C : Type u₁
inst✝⁴ : Category.{v₁, u₁} C
D : Type u₂
inst✝³ : Category.{v₂, u₂} D
J : Type v₁
inst✝² : SmallCategory J
inst✝¹ : FinCategory J
F : C ⥤ D
inst✝ : RepresentablyFlat F
K : J ⥤ C
c : Cone K
hc : IsLimit c
s : Cone (K ⋙ F)
f₁ f₂ : s.pt ⟶ F.obj c.pt
h₁ : ∀ (j : J), f₁ ≫ (F.mapCone c).π.app j = s.π.app j
h₂ : ∀ (j : J), f₂ ≫ (F.mapCone c).π.app j = s.π.app j
α₁ : (F.mapCone c).toStructuredArrow ⋙ map f₁ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
α₂ : (F.mapCone c).toStructuredArrow ⋙ map f₂ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
c₁ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₁ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₁)
c₂ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₂ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₂)
c₀ : Cone (biconeMk J c₁ c₂) := IsCofiltered.cone (biconeMk J c₁ c₂)
g₁ : c₀.pt ⟶ c₁.pt := c₀.π.app Bicone.left
g₂ : c₀.pt ⟶ c₂.pt := c₀.π.app Bicone.right
this✝¹ : ∀ (j : J), g₁.right ≫ c.π.app j = g₂.right ≫ c.π.app j
this✝ : c.extend g₁.right = c.extend g₂.right
this : g₁.right = g₂.right
⊢ 𝟙 s.pt ≫ f₂ = f₂

Tactic:
simp

Result:
no goals

Proof state:
C : Type u₁
inst✝⁴ : Category.{v₁, u₁} C
D : Type u₂
inst✝³ : Category.{v₂, u₂} D
J : Type v₁
inst✝² : SmallCategory J
inst✝¹ : FinCategory J
F : C ⥤ D
inst✝ : RepresentablyFlat F
K : J ⥤ C
c : Cone K
hc : IsLimit c
s : Cone (K ⋙ F)
f₁ f₂ : s.pt ⟶ F.obj c.pt
h₁ : ∀ (j : J), f₁ ≫ (F.mapCone c).π.app j = s.π.app j
h₂ : ∀ (j : J), f₂ ≫ (F.mapCone c).π.app j = s.π.app j
α₁ : (F.mapCone c).toStructuredArrow ⋙ map f₁ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
α₂ : (F.mapCone c).toStructuredArrow ⋙ map f₂ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
c₁ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₁ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₁)
⊢ f₁ = f₂

Tactic:
let c₂ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₂ (pre s.pt K F) :)).obj (c.toStructuredArrowCone F f₂)

Result:
C : Type u₁
inst✝⁴ : Category.{v₁, u₁} C
D : Type u₂
inst✝³ : Category.{v₂, u₂} D
J : Type v₁
inst✝² : SmallCategory J
inst✝¹ : FinCategory J
F : C ⥤ D
inst✝ : RepresentablyFlat F
K : J ⥤ C
c : Cone K
hc : IsLimit c
s : Cone (K ⋙ F)
f₁ f₂ : s.pt ⟶ F.obj c.pt
h₁ : ∀ (j : J), f₁ ≫ (F.mapCone c).π.app j = s.π.app j
h₂ : ∀ (j : J), f₂ ≫ (F.mapCone c).π.app j = s.π.app j
α₁ : (F.mapCone c).toStructuredArrow ⋙ map f₁ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
α₂ : (F.mapCone c).toStructuredArrow ⋙ map f₂ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
c₁ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₁ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₁)
c₂ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₂ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₂)
⊢ f₁ = f₂

Proof state:
C : Type u₁
inst✝⁴ : Category.{v₁, u₁} C
D : Type u₂
inst✝³ : Category.{v₂, u₂} D
J : Type v₁
inst✝² : SmallCategory J
inst✝¹ : FinCategory J
F : C ⥤ D
inst✝ : RepresentablyFlat F
K : J ⥤ C
c : Cone K
hc : IsLimit c
s : Cone (K ⋙ F)
f₁ f₂ : s.pt ⟶ F.obj c.pt
h₁ : ∀ (j : J), f₁ ≫ (F.mapCone c).π.app j = s.π.app j
h₂ : ∀ (j : J), f₂ ≫ (F.mapCone c).π.app j = s.π.app j
α₁ : (F.mapCone c).toStructuredArrow ⋙ map f₁ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
α₂ : (F.mapCone c).toStructuredArrow ⋙ map f₂ ⟶ s.toStructuredArrow := { app := fun X => eqToHom ⋯, naturality := ⋯ }
c₁ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₁ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₁)
c₂ : Cone (s.toStructuredArrow ⋙ pre s.pt K F) :=
  (Cones.postcompose (whiskerRight α₂ (pre s.pt K F))).obj (c.toStructuredArrowCone F f₂)
c₀ : Cone (biconeMk J c₁ c₂) := IsCofiltered.cone (biconeMk J c₁ c₂)
g₁ : c₀.pt ⟶ c₁.pt := c₀.π.app Bicone.left
g₂ : c₀.pt ⟶ c₂.pt := c₀.π.app Bicone.right
this✝¹ : ∀ (j : J), g₁.right ≫ c.π.app j = g₂.right ≫ c.π.app j
this✝ : c.extend g₁.right = c.extend g₂.right
this : g₁.right = g₂.right
⊢ f₁ = f₂

Tactic:
calc
  f₁ = 𝟙 _ ≫ f₁ := by simp
  _ = c₀.pt.hom ≫ F.map g₁.right := g₁.w
  _ = c₀.pt.hom ≫ F.map g₂.right := by rw [this]
  _ = 𝟙 _ ≫ f₂ := g₂.w.symm
  _ = f₂ := by simp

Result:
no goals