-- Mathlib/CategoryTheory/Subobject/Comma.lean
theorem lift_projectSubobject [HasFiniteLimits C] [PreservesFiniteLimits T]
    {A : StructuredArrow S T} :
    ∀ (P : Subobject A) {q} (hq : q ≫ T.map (projectSubobject P).arrow = A.hom),
      liftSubobject (projectSubobject P) hq = P :=
  Subobject.ind _
    (by
      intro P f hf q hq
      fapply Subobject.mk_eq_mk_of_comm
      · fapply isoMk
        · exact Subobject.underlyingIso _
        · exact (cancel_mono (T.map f.right)).1 (by dsimp; simpa [← T.map_comp] using hq)
      · exact ext _ _ (by dsimp; simp))

Proof state:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A : StructuredArrow S T
⊢ ∀ ⦃A_1 : StructuredArrow S T⦄ (f : A_1 ⟶ A) [inst : Mono f]
    {q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))}
    (hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom),
    liftSubobject (projectSubobject (Subobject.mk f)) hq = Subobject.mk f

Tactic:
intro P f hf q hq

Result:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ liftSubobject (projectSubobject (Subobject.mk f)) hq = Subobject.mk f

Proof state:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ ((isoMk (Subobject.underlyingIso (MonoOver.mk' f).arrow.right) ⋯).hom ≫ f).right =
    (homMk (projectSubobject (Subobject.mk f)).arrow hq).right

Tactic:
dsimp

Result:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ (Subobject.underlyingIso f.right).hom ≫ f.right = (Subobject.mk f.right).arrow

Proof state:
case i.w
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ autoParam ((mk q).hom ≫ T.map (Subobject.underlyingIso (MonoOver.mk' f).arrow.right).hom = P.hom) _auto✝

Tactic:
exact (cancel_mono (T.map f.right)).1 (by dsimp; simpa [← T.map_comp] using hq)

Result:
no goals

Proof state:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ liftSubobject (projectSubobject (Subobject.mk f)) hq = Subobject.mk f

Tactic:
fapply Subobject.mk_eq_mk_of_comm

Result:
case i
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ mk q ≅ P

case w
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ Iso.hom ?i ≫ f = homMk (projectSubobject (Subobject.mk f)).arrow hq

Proof state:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ ((mk q).hom ≫ T.map (Subobject.underlyingIso (MonoOver.mk' f).arrow.right).hom) ≫ T.map f.right =
    P.hom ≫ T.map f.right

Tactic:
dsimp

Result:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ (q ≫ T.map (Subobject.underlyingIso f.right).hom) ≫ T.map f.right = P.hom ≫ T.map f.right

Proof state:
case i
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ mk q ≅ P

Tactic:
fapply isoMk

Result:
case i.g
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ (mk q).right ≅ P.right

case i.w
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ autoParam ((mk q).hom ≫ T.map (Iso.hom ?i.g) = P.hom) _auto✝

Proof state:
case i.g
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ (mk q).right ≅ P.right

Tactic:
exact Subobject.underlyingIso _

Result:
no goals

Proof state:
C : Type u₁
inst✝³ : Category.{v₁, u₁} C
D : Type u₂
inst✝² : Category.{v₂, u₂} D
S : D
T : C ⥤ D
inst✝¹ : HasFiniteLimits C
inst✝ : PreservesFiniteLimits T
A P : StructuredArrow S T
f : P ⟶ A
hf : Mono f
q : (Functor.fromPUnit S).obj A.left ⟶ T.obj (Subobject.underlying.obj (projectSubobject (Subobject.mk f)))
hq : q ≫ T.map (projectSubobject (Subobject.mk f)).arrow = A.hom
⊢ (Subobject.underlyingIso f.right).hom ≫ f.right = (Subobject.mk f.right).arrow

Tactic:
simp

Result:
no goals