-- Lean 4 proof step from Mathlib.CategoryTheory.Limits.FilteredColimitCommutesProduct (goal)
Goal:
α : Type u
I : α → Type u
inst : (i : α) → SmallCategory (I i)
inst_1 : ∀ (i : α), IsFiltered.{u, u} (I i)
F : (i : α) → I i ⥤ Type u
y y' : (fun (X : Type u) ↦ X) (colimit (pointwiseProduct (I := I) F))
hy :
  Eq (α := (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
    ((hom (FC := TypeCat.Fun) (colimitPointwiseProductToProductColimit (I := I) F) :
          (a : (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F))) →
            (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
        y :
      (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
    ((hom (FC := TypeCat.Fun) (colimitPointwiseProductToProductColimit (I := I) F) :
          (a : (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F))) →
            (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
        y' :
      (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
ky : (i : α) → I i
yk₀ : (pointwiseProduct (I := I) F).obj ky
hyk₀ :
  (hom (FC := TypeCat.Fun) (colimit.ι (pointwiseProduct (I := I) F) ky) :
        (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj ky)) →
          (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F)))
      yk₀ =
    y
ky' : (i : α) → I i
yk₀' : (pointwiseProduct (I := I) F).obj ky'
hyk₀' :
  (hom (FC := TypeCat.Fun) (colimit.ι (pointwiseProduct (I := I) F) ky') :
        (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj ky')) →
          (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F)))
      yk₀' =
    y'
k : (i : α) → I i := IsFiltered.max ky ky'
yk : (pointwiseProduct (I := I) F).obj k :=
  (hom (FC := TypeCat.Fun) ((pointwiseProduct (I := I) F).map (IsFiltered.leftToMax ky ky')) :
      (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj ky)) →
        (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj (IsFiltered.max ky ky')))
    yk₀
yk' : (pointwiseProduct (I := I) F).obj k :=
  (hom (FC := TypeCat.Fun) ((pointwiseProduct (I := I) F).map (IsFiltered.rightToMax ky ky')) :
      (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj ky')) →
        (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj (IsFiltered.max ky ky')))
    yk₀'
⊢ y = y'
have refine_1 : ∀
  (hy :
    Eq (α := (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
      ((hom (FC := TypeCat.Fun) (colimitPointwiseProductToProductColimit (I := I) F) :
            (a : (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F))) →
              (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
          ((hom (FC := TypeCat.Fun) (colimit.ι (pointwiseProduct (I := I) F) k) :
                (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj k)) →
                  (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F)))
              yk :
            (fun (X : Type u) ↦ X) (colimit (pointwiseProduct (I := I) F))) :
        (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
      ((hom (FC := TypeCat.Fun) (colimitPointwiseProductToProductColimit (I := I) F) :
            (a : (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F))) →
              (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s)))
          y' :
        (fun (X : Type u) ↦ X) (∏ᶜ fun (s : α) ↦ colimit (F s))))
  (hyk₀ :
    Eq (α := (fun (X : Type u) ↦ X) (colimit (pointwiseProduct (I := I) F)))
      ((hom (FC := TypeCat.Fun) (colimit.ι (pointwiseProduct (I := I) F) ky) :
            (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj ky)) →
              (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F)))
          yk₀ :
        (fun (X : Type u) ↦ X) (colimit (pointwiseProduct (I := I) F)))
      ((hom (FC := TypeCat.Fun) (colimit.ι (pointwiseProduct (I := I) F) k) :
            (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj k)) →
              (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F)))
          yk :
        (fun (X : Type u) ↦ X) (colimit (pointwiseProduct (I := I) F)))),
  (hom (FC := TypeCat.Fun) (colimit.ι (pointwiseProduct (I := I) F) k) :
        (a : (fun (X : Type u) ↦ X) ((pointwiseProduct F).obj k)) →
          (fun (X : Type u) ↦ X) (colimit (pointwiseProduct F)))
      yk =
    y'
Tactic: obtain rfl : y = colimit.ι (pointwiseProduct F) k yk := by
      simp only [k, yk, colimit.w_apply, hyk₀]
Cleared hypotheses: y, hy, hyk₀