∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Preadditive C]
  {F G K : CochainComplex C ℤ} {n₁ n₂ n₁₂ : ℤ} (z₁ : CochainComplex.HomComplex.Cochain F G n₁)
  (z₂ : CochainComplex.HomComplex.Cochain G K n₂) (h : n₁ + n₂ = n₁₂), z₁.comp (-z₂) h = -z₁.comp z₂ h