-- Mathlib/CategoryTheory/Triangulated/Pretriangulated.lean
/-- Any morphism `Z ⟶ X⟦1⟧` is part of a distinguished triangle `X ⟶ Y ⟶ Z ⟶ X⟦1⟧` -/
lemma distinguished_cocone_triangle₂ {Z X : C} (h : Z ⟶ X⟦(1 : ℤ)⟧) :
    ∃ (Y : C) (f : X ⟶ Y) (g : Y ⟶ Z), Triangle.mk f g h ∈ distTriang C

Proof state:
case intro.intro.intro
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h ≅ (Triangle.mk h f' g').invRotate.invRotate

Tactic:
exact Triangle.isoMk _ _ ((shiftEquiv C (1 : ℤ)).unitIso.app X) (Iso.refl _) (Iso.refl _)
  (by aesop_cat) (by aesop_cat)
  (by dsimp; simp only [shift_shiftFunctorCompIsoId_inv_app, id_comp])

Result:
no goals

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ h ≫ (shiftFunctor C 1).map ((shiftFunctorCompIsoId C 1 (-1) ⋯).inv.app X) =
    𝟙 Z ≫ h ≫ (shiftFunctorCompIsoId C (-1) 1 ⋯).inv.app ((shiftFunctor C 1).obj X)

Tactic:
simp only [shift_shiftFunctorCompIsoId_inv_app, id_comp]

Result:
no goals

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ (Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h).mor₃ ≫
      (shiftFunctor C 1).map ((shiftEquiv C 1).unitIso.app X).hom =
    (Iso.refl (Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h).obj₃).hom ≫
      (Triangle.mk h f' g').invRotate.invRotate.mor₃

Tactic:
dsimp

Result:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ h ≫ (shiftFunctor C 1).map ((shiftFunctorCompIsoId C 1 (-1) ⋯).inv.app X) =
    𝟙 Z ≫ h ≫ (shiftFunctorCompIsoId C (-1) 1 ⋯).inv.app ((shiftFunctor C 1).obj X)

Proof state:
case intro.intro.intro
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ ∃ Y f g, Triangle.mk f g h ∈ distinguishedTriangles

Tactic:
refine ⟨T'.obj₂, ((shiftEquiv C (1 : ℤ)).unitIso.app X).hom ≫ T'.mor₁, T'.mor₂,
  isomorphic_distinguished _ (inv_rot_of_distTriang _ (inv_rot_of_distTriang _ mem)) _ ?_⟩

Result:
case intro.intro.intro
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h ≅ (Triangle.mk h f' g').invRotate.invRotate

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ (Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h).mor₂ ≫
      (Iso.refl (Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h).obj₃).hom =
    (Iso.refl (Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h).obj₂).hom ≫
      (Triangle.mk h f' g').invRotate.invRotate.mor₂

Tactic:
aesop_cat

Result:
no goals

Proof state:
case intro.intro.intro
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
⊢ ∃ Y f g, Triangle.mk f g h ∈ distinguishedTriangles

Tactic:
let T' := (Triangle.mk h f' g').invRotate.invRotate

Result:
case intro.intro.intro
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ ∃ Y f g, Triangle.mk f g h ∈ distinguishedTriangles

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
⊢ ∃ Y f g, Triangle.mk f g h ∈ distinguishedTriangles

Tactic:
obtain ⟨Y', f', g', mem⟩ := distinguished_cocone_triangle h

Result:
case intro.intro.intro
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
⊢ ∃ Y f g, Triangle.mk f g h ∈ distinguishedTriangles

Proof state:
C : Type u
inst✝⁴ : Category.{v, u} C
inst✝³ : HasZeroObject C
inst✝² : HasShift C ℤ
inst✝¹ : Preadditive C
inst✝ : ∀ (n : ℤ), (shiftFunctor C n).Additive
hC : Pretriangulated C
Z X : C
h : Z ⟶ (shiftFunctor C 1).obj X
Y' : C
f' : (shiftFunctor C 1).obj X ⟶ Y'
g' : Y' ⟶ (shiftFunctor C 1).obj Z
mem : Triangle.mk h f' g' ∈ distinguishedTriangles
T' : Triangle C := (Triangle.mk h f' g').invRotate.invRotate
⊢ (Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h).mor₁ ≫
      (Iso.refl (Triangle.mk (((shiftEquiv C 1).unitIso.app X).hom ≫ T'.mor₁) T'.mor₂ h).obj₂).hom =
    ((shiftEquiv C 1).unitIso.app X).hom ≫ (Triangle.mk h f' g').invRotate.invRotate.mor₁

Tactic:
aesop_cat

Result:
no goals