-- Mathlib/CategoryTheory/Shift/Adjunction.lean
/-- Given an adjunction `adj : F ⊣ G`, `a` in `A` and commutation isomorphisms
`e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a` and
`e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a`, if `e₁` and `e₂` are compatible with the
counit of the adjunction `adj`, then we get a formula for `e₁.hom` in terms of `e₂`.
-/
lemma compatibilityCounit_left (h : CompatibilityCounit adj e₁ e₂) (X : C) :
    e₁.hom.app X = F.map ((adj.unit.app X)⟦a⟧') ≫ F.map (e₂.inv.app _) ≫ adj.counit.app _

Proof state:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X =
    e₁.hom.app ((𝟭 C).obj X) ≫
      (F ⋙ shiftFunctor D a).map (adj.unit.app X) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))

Tactic:
rw [Functor.comp_map, ← Functor.map_comp, left_triangle_components]

Result:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X = e₁.hom.app ((𝟭 C).obj X) ≫ (shiftFunctor D a).map (𝟙 (F.obj X))

Proof state:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X = e₁.hom.app ((𝟭 C).obj X) ≫ (shiftFunctor D a).map (𝟙 (F.obj X))

Tactic:
simp only [Functor.comp_obj, Functor.id_obj, Functor.map_id, comp_id]

Result:
no goals

Proof state:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X =
    F.map ((shiftFunctor C a).map (adj.unit.app X)) ≫
      e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))

Tactic:
erw [e₁.hom.naturality_assoc]

Result:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X =
    e₁.hom.app ((𝟭 C).obj X) ≫
      (F ⋙ shiftFunctor D a).map (adj.unit.app X) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))

Proof state:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X =
    F.map ((shiftFunctor C a).map (adj.unit.app X)) ≫
      F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X))

Tactic:
rw [this]

Result:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X =
    F.map ((shiftFunctor C a).map (adj.unit.app X)) ≫
      e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))

Proof state:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
⊢ e₁.hom.app X =
    F.map ((shiftFunctor C a).map (adj.unit.app X)) ≫
      F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X))

Tactic:
have := h (F.obj X)

Result:
C : Type u_1
D : Type u_2
inst✝⁴ : Category.{u_4, u_1} C
inst✝³ : Category.{u_5, u_2} D
F : C ⥤ D
G : D ⥤ C
adj : F ⊣ G
A : Type u_3
inst✝² : AddMonoid A
inst✝¹ : HasShift C A
inst✝ : HasShift D A
a : A
e₁ : shiftFunctor C a ⋙ F ≅ F ⋙ shiftFunctor D a
e₂ : shiftFunctor D a ⋙ G ≅ G ⋙ shiftFunctor C a
h : CompatibilityCounit adj e₁ e₂
X : C
this :
  adj.counit.app ((shiftFunctor D a).obj (F.obj X)) =
    F.map (e₂.hom.app (F.obj X)) ≫ e₁.hom.app (G.obj (F.obj X)) ≫ (shiftFunctor D a).map (adj.counit.app (F.obj X))
⊢ e₁.hom.app X =
    F.map ((shiftFunctor C a).map (adj.unit.app X)) ≫
      F.map (e₂.inv.app (F.obj X)) ≫ adj.counit.app ((shiftFunctor D a).obj (F.obj X))