∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {J : CategoryTheory.GrothendieckTopology C}
  [inst_1 : CategoryTheory.HasWeakSheafify J (Type v)] [inst_2 : CategoryTheory.HasSheafify J AddCommGrpCat]
  (S : J.MayerVietorisSquare),
  S.shortComplex.g =
    CategoryTheory.Limits.biprod.desc
      ((CategoryTheory.presheafToSheaf J AddCommGrpCat).map
        (CategoryTheory.Functor.whiskerRight (CategoryTheory.yoneda.map S.f₂₄) AddCommGrpCat.free))
      ((CategoryTheory.presheafToSheaf J AddCommGrpCat).map
        (CategoryTheory.Functor.whiskerRight (CategoryTheory.yoneda.map S.f₃₄) AddCommGrpCat.free))