∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] (X : CategoryTheory.Limits.FormalCoproduct C) (i : X.I)
  {Z : CategoryTheory.Limits.FormalCoproduct C} (h : X ⟶ Z),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.Sigma.ι X.toFun i)
      (CategoryTheory.CategoryStruct.comp X.coproductIsoSelf.hom h) =
    CategoryTheory.CategoryStruct.comp
      (CategoryTheory.Limits.FormalCoproduct.Hom.fromIncl i (CategoryTheory.CategoryStruct.id (X.obj i))) h