Module: Mathlib.CategoryTheory.Sites.Hypercover.One

Goal state before:
pp: case refine_2
C : Type u
inst✝³ : Category.{v, u} C
A : Type u_1
inst✝² : Category.{v_1, u_1} A
S : C
E : PreOneHypercover S
c : Cofan E.X
hc : IsColimit c
d : Cofan E.Y'
hd : IsColimit d
F : Cᵒᵖ ⥤ A
inst✝¹ : PreservesLimit (Discrete.functor fun i ↦ op (E.X i)) F
inst✝ : PreservesLimit (Discrete.functor fun i ↦ op (E.Y' i)) F
c' : Fan (E.multicospanIndex F).left := Fan.mk (F.obj (op c.pt)) fun i ↦ F.map (c.inj i).op
hc' : IsLimit c' := isLimitFanMkObjOfIsLimit F (fun i ↦ op (E.X i)) (fun i ↦ (c.inj i).op) (Cofan.IsColimit.op hc)
d' : Fan (E.multicospanIndex F).right := Fan.mk (F.obj (op d.pt)) fun i ↦ F.map (d.inj i).op
hd' : IsLimit d' := isLimitFanMkObjOfIsLimit F (fun i ↦ op (E.Y' i)) (fun i ↦ (d.inj i).op) (Cofan.IsColimit.op hd)
⊢ (Iso.refl c'.pt).hom ≫ F.map (Cofan.IsColimit.desc hd fun x ↦ E.p₂ x.snd ≫ c.inj x.fst.2).op =
    (E.multicospanIndex F).sndPiMapOfIsLimit c' hd' ≫ (Iso.refl d'.pt).hom

pp: case refine_3
C : Type u
inst✝³ : Category.{v, u} C
A : Type u_1
inst✝² : Category.{v_1, u_1} A
S : C
E : PreOneHypercover S
c : Cofan E.X
hc : IsColimit c
d : Cofan E.Y'
hd : IsColimit d
F : Cᵒᵖ ⥤ A
inst✝¹ : PreservesLimit (Discrete.functor fun i ↦ op (E.X i)) F
inst✝ : PreservesLimit (Discrete.functor fun i ↦ op (E.Y' i)) F
c' : Fan (E.multicospanIndex F).left := Fan.mk (F.obj (op c.pt)) fun i ↦ F.map (c.inj i).op
hc' : IsLimit c' := isLimitFanMkObjOfIsLimit F (fun i ↦ op (E.X i)) (fun i ↦ (c.inj i).op) (Cofan.IsColimit.op hc)
d' : Fan (E.multicospanIndex F).right := Fan.mk (F.obj (op d.pt)) fun i ↦ F.map (d.inj i).op
hd' : IsLimit d' := isLimitFanMkObjOfIsLimit F (fun i ↦ op (E.Y' i)) (fun i ↦ (d.inj i).op) (Cofan.IsColimit.op hd)
⊢ (Iso.refl (((E.multicospanIndex F).multiforkEquivPiForkOfIsLimit hc' hd').functor.obj (E.multifork F)).pt).hom ≫
      (E.forkOfIsColimit hc hd F).ι =
    Fork.ι (((E.multicospanIndex F).multiforkEquivPiForkOfIsLimit hc' hd').functor.obj (E.multifork F)) ≫
      (Iso.refl c'.pt).hom

Tactic:
· refine Fan.IsLimit.hom_ext hd' _ _ fun i ↦ ?_
    simp only [multicospanShape_L, multicospanIndex_right, multicospanShape_R, Iso.refl_hom,
      Y'_apply, id_comp, comp_id]
    rw [MulticospanIndex.sndPiMapOfIsLimit_proj]
    simp [c', d', ← F.map_comp, ← op_comp]

Goal state after:
case refine_3
C : Type u
inst✝³ : Category.{v, u} C
A : Type u_1
inst✝² : Category.{v_1, u_1} A
S : C
E : PreOneHypercover S
c : Cofan E.X
hc : IsColimit c
d : Cofan E.Y'
hd : IsColimit d
F : Cᵒᵖ ⥤ A
inst✝¹ : PreservesLimit (Discrete.functor fun i ↦ op (E.X i)) F
inst✝ : PreservesLimit (Discrete.functor fun i ↦ op (E.Y' i)) F
c' : Fan (E.multicospanIndex F).left := Fan.mk (F.obj (op c.pt)) fun i ↦ F.map (c.inj i).op
hc' : IsLimit c' := isLimitFanMkObjOfIsLimit F (fun i ↦ op (E.X i)) (fun i ↦ (c.inj i).op) (Cofan.IsColimit.op hc)
d' : Fan (E.multicospanIndex F).right := Fan.mk (F.obj (op d.pt)) fun i ↦ F.map (d.inj i).op
hd' : IsLimit d' := isLimitFanMkObjOfIsLimit F (fun i ↦ op (E.Y' i)) (fun i ↦ (d.inj i).op) (Cofan.IsColimit.op hd)
⊢ (Iso.refl (((E.multicospanIndex F).multiforkEquivPiForkOfIsLimit hc' hd').functor.obj (E.multifork F)).pt).hom ≫
      (E.forkOfIsColimit hc hd F).ι =
    Fork.ι (((E.multicospanIndex F).multiforkEquivPiForkOfIsLimit hc' hd').functor.obj (E.multifork F)) ≫
      (Iso.refl c'.pt).hom