-- Mathlib/CategoryTheory/Sites/CompatiblePlus.lean
theorem whiskerRight_toPlus_comp_plusCompIso_hom :
    whiskerRight (J.toPlus _) _ ≫ (J.plusCompIso F P).hom = J.toPlus _

Proof state:
case w.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
⊢ (whiskerRight (J.toPlus P) F ≫ (J.plusCompIso F P).hom).app x✝ = (J.toPlus (P ⋙ F)).app x✝

Tactic:
dsimp [toPlus]

Result:
case w.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
⊢ F.map (⊤.toMultiequalizer P ≫ colimit.ι (J.diagram P (unop x✝)) (op ⊤)) ≫ (J.plusCompIso F P).hom.app x✝ =
    ⊤.toMultiequalizer (P ⋙ F) ≫ colimit.ι (J.diagram (P ⋙ F) (unop x✝)) (op ⊤)

Proof state:
case w.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
⊢ F.map (⊤.toMultiequalizer P) ≫
      (J.diagramCompIso F P (unop x✝)).hom.app (op ⊤) ≫ colimit.ι (J.diagram (P ⋙ F) (unop x✝)) (op ⊤) =
    ⊤.toMultiequalizer (P ⋙ F) ≫ colimit.ι (J.diagram (P ⋙ F) (unop x✝)) (op ⊤)

Tactic:
simp only [← Category.assoc]

Result:
case w.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
⊢ (F.map (⊤.toMultiequalizer P) ≫ (J.diagramCompIso F P (unop x✝)).hom.app (op ⊤)) ≫
      colimit.ι (J.diagram (P ⋙ F) (unop x✝)) (op ⊤) =
    ⊤.toMultiequalizer (P ⋙ F) ≫ colimit.ι (J.diagram (P ⋙ F) (unop x✝)) (op ⊤)

Proof state:
case w.h.e_a.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
a : (unop (op ⊤)).shape.L
⊢ F.map (⊤.toMultiequalizer P ≫ Multiequalizer.ι ((unop (op ⊤)).index P) a) =
    ⊤.toMultiequalizer (P ⋙ F) ≫ Multiequalizer.ι ((unop (op ⊤)).index (P ⋙ F)) a

Tactic:
simp only [unop_op, limit.lift_π, Multifork.ofι_π_app, Functor.comp_obj, Functor.comp_map]

Result:
no goals

Proof state:
case w.h.e_a.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
⊢ ∀ (a : (unop (op ⊤)).shape.L),
    (F.map (⊤.toMultiequalizer P) ≫ (J.diagramCompIso F P (unop x✝)).hom.app (op ⊤)) ≫
        Multiequalizer.ι ((unop (op ⊤)).index (P ⋙ F)) a =
      ⊤.toMultiequalizer (P ⋙ F) ≫ Multiequalizer.ι ((unop (op ⊤)).index (P ⋙ F)) a

Tactic:
intro a

Result:
case w.h.e_a.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
a : (unop (op ⊤)).shape.L
⊢ (F.map (⊤.toMultiequalizer P) ≫ (J.diagramCompIso F P (unop x✝)).hom.app (op ⊤)) ≫
      Multiequalizer.ι ((unop (op ⊤)).index (P ⋙ F)) a =
    ⊤.toMultiequalizer (P ⋙ F) ≫ Multiequalizer.ι ((unop (op ⊤)).index (P ⋙ F)) a

Proof state:
case w.h.e_a
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
⊢ F.map (⊤.toMultiequalizer P) ≫ (J.diagramCompIso F P (unop x✝)).hom.app (op ⊤) = ⊤.toMultiequalizer (P ⋙ F)

Tactic:
apply Multiequalizer.hom_ext

Result:
case w.h.e_a.h
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) (W : J.Cover X) (P : Cᵒᵖ ⥤ D), PreservesLimit (W.index P).multicospan F
P : Cᵒᵖ ⥤ D
inst✝² : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
inst✝¹ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ E
inst✝ : ∀ (X : C), PreservesColimitsOfShape (J.Cover X)ᵒᵖ F
x✝ : Cᵒᵖ
⊢ ∀ (a : (unop (op ⊤)).shape.L),
    (F.map (⊤.toMultiequalizer P) ≫ (J.diagramCompIso F P (unop x✝)).hom.app (op ⊤)) ≫
        Multiequalizer.ι ((unop (op ⊤)).index (P ⋙ F)) a =
      ⊤.toMultiequalizer (P ⋙ F) ≫ Multiequalizer.ι ((unop (op ⊤)).index (P ⋙ F)) a