-- Mathlib/CategoryTheory/Sites/Plus.lean
theorem plusMap_toPlus : J.plusMap (J.toPlus P) = J.toPlus (J.plusObj P)

Proof state:
case h.e'_2.h
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
X : Cᵒᵖ
S : (J.Cover (unop X))ᵒᵖ
e : unop S ⟶ ⊤ := homOfLE ⋯
I : (unop S).shape.L
ee : (J.pullback (Cover.Arrow.map I e).f).obj (unop S) ⟶ ⊤ := homOfLE ⋯
II : (unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).shape.L
e_1✝ :
  ((J.diagram P (unop X)).obj S ⟶ ((unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).index P).left II) =
    (multiequalizer ((unop S).index P) ⟶
      ((unop S).index P).right
        { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } })
⊢ ((Multiequalizer.ι ((unop S).index P) I ≫ ⊤.toMultiequalizer P) ≫ (J.diagram P I.Y).map ee.op) ≫
      Multiequalizer.ι ((unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).index P) II =
    Multiequalizer.ι ((unop S).index P)
        ((unop S).shape.fst
          { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } }) ≫
      ((unop S).index P).fst
        { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } }

case h.e'_3.h
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
X : Cᵒᵖ
S : (J.Cover (unop X))ᵒᵖ
e : unop S ⟶ ⊤ := homOfLE ⋯
I : (unop S).shape.L
ee : (J.pullback (Cover.Arrow.map I e).f).obj (unop S) ⟶ ⊤ := homOfLE ⋯
II : (unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).shape.L
e_1✝ :
  ((J.diagram P (unop X)).obj S ⟶ ((unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).index P).left II) =
    (multiequalizer ((unop S).index P) ⟶
      ((unop S).index P).right
        { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } })
⊢ Multiequalizer.lift ((unop ((J.pullback (Cover.Arrow.map I e.op.unop).f.op.unop).op.obj S)).index P)
        ((J.diagram P (unop X)).obj S) (fun I_1 => Multiequalizer.ι ((unop S).index P) (Cover.Arrow.base I_1)) ⋯ ≫
      Multiequalizer.ι ((unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).index P) II =
    Multiequalizer.ι ((unop S).index P)
        ((unop S).shape.snd
          { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } }) ≫
      ((unop S).index P).snd
        { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } }

Tactic:
all_goals dsimp; simp

Result:
no goals

Proof state:
case h.e'_3.h
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
X : Cᵒᵖ
S : (J.Cover (unop X))ᵒᵖ
e : unop S ⟶ ⊤ := homOfLE ⋯
I : (unop S).shape.L
ee : (J.pullback (Cover.Arrow.map I e).f).obj (unop S) ⟶ ⊤ := homOfLE ⋯
II : (unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).shape.L
e_1✝ :
  ((J.diagram P (unop X)).obj S ⟶ ((unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).index P).left II) =
    (multiequalizer ((unop S).index P) ⟶
      ((unop S).index P).right
        { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } })
⊢ Multiequalizer.lift ((unop ((J.pullback (Cover.Arrow.map I e.op.unop).f.op.unop).op.obj S)).index P)
        ((J.diagram P (unop X)).obj S) (fun I_1 => Multiequalizer.ι ((unop S).index P) (Cover.Arrow.base I_1)) ⋯ ≫
      Multiequalizer.ι ((unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).index P) II =
    Multiequalizer.ι ((unop S).index P)
        ((unop S).shape.snd
          { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } }) ≫
      ((unop S).index P).snd
        { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } }

Tactic:
dsimp

Result:
case h.e'_3.h
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
X : Cᵒᵖ
S : (J.Cover (unop X))ᵒᵖ
e : unop S ⟶ ⊤ := homOfLE ⋯
I : (unop S).shape.L
ee : (J.pullback (Cover.Arrow.map I e).f).obj (unop S) ⟶ ⊤ := homOfLE ⋯
II : (unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).shape.L
e_1✝ :
  ((J.diagram P (unop X)).obj S ⟶ ((unop (op ((J.pullback (Cover.Arrow.map I e).f).obj (unop S)))).index P).left II) =
    (multiequalizer ((unop S).index P) ⟶
      ((unop S).index P).right
        { fst := I, snd := Cover.Arrow.base II, r := { Z := II.Y, g₁ := II.f, g₂ := 𝟙 II.Y, w := ⋯ } })
⊢ Multiequalizer.lift (((unop S).pullback I.f).index P) (multiequalizer ((unop S).index P))
        (fun I_1 => Multiequalizer.ι ((unop S).index P) I_1.base) ⋯ ≫
      Multiequalizer.ι (((unop S).pullback I.f).index P) II =
    Multiequalizer.ι ((unop S).index P) (Cover.Arrow.base II) ≫ P.map (𝟙 (op II.Y))

Proof state:
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
⊢ J.plusMap (J.toPlus P) = J.toPlus (J.plusObj P)

Tactic:
ext X : 2

Result:
case w.h
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
X : Cᵒᵖ
⊢ (J.plusMap (J.toPlus P)).app X = (J.toPlus (J.plusObj P)).app X

Proof state:
case w.h.e_a
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
X : Cᵒᵖ
S : (J.Cover (unop X))ᵒᵖ
e : unop S ⟶ ⊤ := homOfLE ⋯
I : (unop S).shape.L
⊢ (J.diagramNatTrans { app := fun X => ⊤.toMultiequalizer P ≫ colimit.ι (J.diagram P (unop X)) (op ⊤), naturality := ⋯ }
            (unop X)).app
        S ≫
      Multiequalizer.ι ((unop S).index (J.plusObj P)) I =
    ((colimit.ι (J.diagram P (unop X)) S ≫ ⊤.toMultiequalizer (J.plusObj P)) ≫
        (J.diagram (J.plusObj P) (unop X)).map e.op) ≫
      Multiequalizer.ι ((unop S).index (J.plusObj P)) I

Tactic:
erw [Multiequalizer.lift_ι]

Result:
case w.h.e_a
C : Type u
inst✝³ : Category.{v, u} C
J : GrothendieckTopology C
D : Type w
inst✝² : Category.{max v u, w} D
inst✝¹ : ∀ (P : Cᵒᵖ ⥤ D) (X : C) (S : J.Cover X), HasMultiequalizer (S.index P)
P : Cᵒᵖ ⥤ D
inst✝ : ∀ (X : C), HasColimitsOfShape (J.Cover X)ᵒᵖ D
X : Cᵒᵖ
S : (J.Cover (unop X))ᵒᵖ
e : unop S ⟶ ⊤ := homOfLE ⋯
I : (unop S).shape.L
⊢ Multiequalizer.ι ((unop S).index P) I ≫
      { app := fun X => ⊤.toMultiequalizer P ≫ colimit.ι (J.diagram P (unop X)) (op ⊤), naturality := ⋯ }.app (op I.Y) =
    ((colimit.ι (J.diagram P (unop X)) S ≫ ⊤.toMultiequalizer (J.plusObj P)) ≫
        (J.diagram (J.plusObj P) (unop X)).map e.op) ≫
      Multiequalizer.ι ((unop S).index (J.plusObj P)) I