Module: Mathlib.CategoryTheory.Limits.Constructions.FiniteProductsOfBinaryProducts

Goal state before:
pp: C : Type u
inst✝⁴ : Category.{v, u} C
D : Type u'
inst✝³ : Category.{v', u'} D
F : C ⥤ D
inst✝² : PreservesColimitsOfShape (Discrete WalkingPair) F
inst✝¹ : PreservesColimitsOfShape (Discrete PEmpty.{1}) F
inst✝ : HasFiniteCoproducts C
n : ℕ
this✝ : ∀ (f : Fin n → C), PreservesColimit (Discrete.functor f) F
f : Fin (n + 1) → C
this : IsColimit
  (extendCofan (Cofan.mk (F.obj (∐ fun i ↦ f i.succ)) fun j ↦ F.map (Sigma.ι (fun i ↦ f i.succ) j))
    (BinaryCofan.mk (F.map coprod.inl) (F.map coprod.inr))) := ⋯
⊢ ∀ (j : Discrete (Fin (n + 1))),
    (extendCofan (Cofan.mk (F.obj (∐ fun i ↦ f i.succ)) fun j ↦ F.map (Sigma.ι (fun i ↦ f i.succ) j))
                (BinaryCofan.mk (F.map coprod.inl) (F.map coprod.inr))).ι.app
          j ≫
        (Iso.refl
            (extendCofan (Cofan.mk (F.obj (∐ fun i ↦ f i.succ)) fun j ↦ F.map (Sigma.ι (fun i ↦ f i.succ) j))
                (BinaryCofan.mk (F.map coprod.inl) (F.map coprod.inr))).pt).hom =
      (Cofan.mk (F.obj (colimit.cocone (pair (f 0) (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).pt)).pt) fun j ↦
              F.map
                (Fin.cases
                  (BinaryCofan.inl
                    (colimit.cocone (pair (f 0) (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).pt)))
                  (fun i ↦
                    (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).ι.app { as := i } ≫
                      BinaryCofan.inr
                        (colimit.cocone (pair (f 0) (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).pt)))
                  j)).ι.app
        j

Tactic:
rintro ⟨j⟩

Goal state after:
C : Type u
inst✝⁴ : Category.{v, u} C
D : Type u'
inst✝³ : Category.{v', u'} D
F : C ⥤ D
inst✝² : PreservesColimitsOfShape (Discrete WalkingPair) F
inst✝¹ : PreservesColimitsOfShape (Discrete PEmpty.{1}) F
inst✝ : HasFiniteCoproducts C
n : ℕ
this✝ : ∀ (f : Fin n → C), PreservesColimit (Discrete.functor f) F
f : Fin (n + 1) → C
this : IsColimit
  (extendCofan (Cofan.mk (F.obj (∐ fun i ↦ f i.succ)) fun j ↦ F.map (Sigma.ι (fun i ↦ f i.succ) j))
    (BinaryCofan.mk (F.map coprod.inl) (F.map coprod.inr))) :=
  extendCofanIsColimit (fun i ↦ F.obj (f i)) (isColimitOfHasCoproductOfPreservesColimit F fun i ↦ f i.succ)
    (isColimitOfHasBinaryCoproductOfPreservesColimit F (f 0) (∐ fun i ↦ f i.succ))
j : Fin (n + 1)
⊢ (extendCofan (Cofan.mk (F.obj (∐ fun i ↦ f i.succ)) fun j ↦ F.map (Sigma.ι (fun i ↦ f i.succ) j))
              (BinaryCofan.mk (F.map coprod.inl) (F.map coprod.inr))).ι.app
        { as := j } ≫
      (Iso.refl
          (extendCofan (Cofan.mk (F.obj (∐ fun i ↦ f i.succ)) fun j ↦ F.map (Sigma.ι (fun i ↦ f i.succ) j))
              (BinaryCofan.mk (F.map coprod.inl) (F.map coprod.inr))).pt).hom =
    (Cofan.mk (F.obj (colimit.cocone (pair (f 0) (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).pt)).pt) fun j ↦
            F.map
              (Fin.cases
                (BinaryCofan.inl (colimit.cocone (pair (f 0) (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).pt)))
                (fun i ↦
                  (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).ι.app { as := i } ≫
                    BinaryCofan.inr
                      (colimit.cocone (pair (f 0) (colimit.cocone (Discrete.functor fun i ↦ f i.succ)).pt)))
                j)).ι.app
      { as := j }