-- Mathlib/CategoryTheory/Sites/CompatibleSheafification.lean
theorem sheafificationWhiskerRightIso_hom_app :
    (J.sheafificationWhiskerRightIso F).hom.app P = (J.sheafifyCompIso F P).hom

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w₁
inst✝⁷ : Category.{max v u, w₁} D
E : Type w₂
inst✝⁶ : Category.{max v u, w₂} E
F : D ⥤ E
inst✝⁵ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) D
inst✝⁴ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) E
inst✝³ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝¹ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
inst✝ : ∀ (X : C) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
⊢ (J.sheafificationWhiskerRightIso F).hom.app P = (J.sheafifyCompIso F P).hom

Tactic:
dsimp [sheafificationWhiskerRightIso, sheafifyCompIso]

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w₁
inst✝⁷ : Category.{max v u, w₁} D
E : Type w₂
inst✝⁶ : Category.{max v u, w₂} E
F : D ⥤ E
inst✝⁵ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) D
inst✝⁴ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) E
inst✝³ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝¹ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
inst✝ : ∀ (X : C) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
⊢ 𝟙 (J.plusObj (J.plusObj P) ⋙ F) ≫
      (J.plusCompIso F (J.plusObj P)).hom ≫
        (𝟙 (J.plusObj (J.plusObj P ⋙ F)) ≫ J.plusMap (J.plusCompIso F P).hom) ≫ 𝟙 (J.plusObj (J.plusObj (P ⋙ F))) =
    (J.plusCompIso F (J.plusObj P)).hom ≫ J.plusMap (J.plusCompIso F P).hom

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w₁
inst✝⁷ : Category.{max v u, w₁} D
E : Type w₂
inst✝⁶ : Category.{max v u, w₂} E
F : D ⥤ E
inst✝⁵ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) D
inst✝⁴ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) E
inst✝³ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝¹ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
inst✝ : ∀ (X : C) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
⊢ 𝟙 (J.plusObj (J.plusObj P) ⋙ F) ≫
      (J.plusCompIso F (J.plusObj P)).hom ≫
        (𝟙 (J.plusObj (J.plusObj P ⋙ F)) ≫ J.plusMap (J.plusCompIso F P).hom) ≫ 𝟙 (J.plusObj (J.plusObj (P ⋙ F))) =
    (J.plusCompIso F (J.plusObj P)).hom ≫ J.plusMap (J.plusCompIso F P).hom

Tactic:
simp only [Category.id_comp, Category.comp_id]

Result:
C : Type u
inst✝⁸ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w₁
inst✝⁷ : Category.{max v u, w₁} D
E : Type w₂
inst✝⁶ : Category.{max v u, w₂} E
F : D ⥤ E
inst✝⁵ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) D
inst✝⁴ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) E
inst✝³ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝¹ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
inst✝ : ∀ (X : C) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
⊢ 𝟙 (J.plusObj (J.plusObj P) ⋙ F) ≫ (J.plusCompIso F (J.plusObj P)).hom ≫ J.plusMap (J.plusCompIso F P).hom =
    (J.plusCompIso F (J.plusObj P)).hom ≫ J.plusMap (J.plusCompIso F P).hom

Proof state:
C : Type u
inst✝⁸ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w₁
inst✝⁷ : Category.{max v u, w₁} D
E : Type w₂
inst✝⁶ : Category.{max v u, w₂} E
F : D ⥤ E
inst✝⁵ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) D
inst✝⁴ : ∀ (J : MulticospanShape), HasLimitsOfShape (WalkingMulticospan J) E
inst✝³ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝¹ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
inst✝ : ∀ (X : C) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
⊢ 𝟙 (J.plusObj (J.plusObj P) ⋙ F) ≫ (J.plusCompIso F (J.plusObj P)).hom ≫ J.plusMap (J.plusCompIso F P).hom =
    (J.plusCompIso F (J.plusObj P)).hom ≫ J.plusMap (J.plusCompIso F P).hom

Tactic:
erw [Category.id_comp]

Result:
no goals