∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {𝒜 : Type w} {f : 𝒜 → CategoryTheory.Limits.FormalCoproduct C}
  (i : 𝒜),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.Sigma.ι f i)
      (CategoryTheory.Limits.FormalCoproduct.coproductIsoCofanPt 𝒜 f).hom =
    (CategoryTheory.Limits.FormalCoproduct.cofan 𝒜 f).inj i