∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Abelian C]
  {A B X Y : CochainComplex C ℤ} {t : A ⟶ X} {i : A ⟶ B} {p : X ⟶ Y} {b : B ⟶ Y} (sq : CategoryTheory.CommSq t i p b)
  (hsq : (n : ℤ) → ⋯.LiftStruct) {Q : CochainComplex C ℤ} {π : B ⟶ Q} {hπ : CategoryTheory.CategoryStruct.comp i π = 0}
  (hQ : CategoryTheory.Limits.IsColimit (CategoryTheory.Limits.CokernelCofork.ofπ π hπ)) {K : CochainComplex C ℤ}
  {ι : K ⟶ X} {hι : CategoryTheory.CategoryStruct.comp ι p = 0}
  (hK : CategoryTheory.Limits.IsLimit (CategoryTheory.Limits.KernelFork.ofι ι hι)),
  CochainComplex.HomComplex.δ 1 2 (CochainComplex.Lifting.cochain₁ sq hsq hQ hK) = 0