∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] [inst_1 : CategoryTheory.Preadditive C] {ι : Type u_2}
  {c : ComplexShape ι} {F G K : HomologicalComplex C c} (φ : F ⟶ G) [inst_2 : HomologicalComplex.HasHomotopyCofiber φ]
  [inst_3 : DecidableRel c.Rel] (α : G ⟶ K) (hα : Homotopy (CategoryTheory.CategoryStruct.comp φ α) 0) (j : ι),
  ¬c.Rel j (c.next j) →
    (HomologicalComplex.homotopyCofiber.desc φ α hα).f j =
      CategoryTheory.CategoryStruct.comp (HomologicalComplex.homotopyCofiber.sndX φ j) (α.f j)