∀ {ι : Type u_1} {V : Type u} [inst : CategoryTheory.Category.{v, u} V] [inst_1 : CategoryTheory.Preadditive V]
  {c : ComplexShape ι} {C D : HomologicalComplex V c} {k₀ : ι},
  (∀ (l : ι), ¬c.Rel k₀ l) →
    (∀ (l : ι), ¬c.Rel l k₀) → ∀ (h : (i j : ι) → c.Rel j i → (C.X i ⟶ D.X j)), (Homotopy.nullHomotopicMap' h).f k₀ = 0