∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Preadditive C]
  (K L : CochainComplex C ℤ) (n m p : ℤ) (hm : n + 1 = m) (hp : m + 1 = p),
  (CochainComplex.HomComplex.leftHomologyData' K L n m p hm hp).π =
    AddCommGrpCat.ofHom (CochainComplex.HomComplex.CohomologyClass.mkAddMonoidHom K L m)