∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Abelian C]
  (L : CochainComplex C ℤ) (d : ℤ) {K : CochainComplex C ℤ} (f : K ⟶ L),
  ∀ val ∈ {α | (CochainComplex.HomComplex.δ (-1) 0 α).EqUpTo (CochainComplex.HomComplex.Cochain.ofHom f) (d + -1)},
    val ∈
      (fun n =>
          {α | (CochainComplex.HomComplex.δ (-1) 0 α).EqUpTo (CochainComplex.HomComplex.Cochain.ofHom f) (↑n + d - 1)})
        0