∀ {J : Type w} {C : Type u} [inst : CategoryTheory.Category.{v, u} C]
  [inst_1 : CategoryTheory.Limits.HasZeroMorphisms C] (f : J → C) [inst_2 : CategoryTheory.Limits.HasBiproduct f]
  (p : J → Prop) [inst_3 : CategoryTheory.Limits.HasBiproduct (Subtype.restrict p f)] (j : Subtype p),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.Limits.biproduct.toSubtype f p)
      (CategoryTheory.Limits.biproduct.π (Subtype.restrict p f) j) =
    CategoryTheory.Limits.biproduct.π f ↑j