∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.HasShift C ℤ]
  {T₁ T₂ : CategoryTheory.Pretriangulated.Triangle C} [inst_2 : CategoryTheory.Preadditive C]
  [inst_3 : ∀ (n : ℤ), (CategoryTheory.shiftFunctor C n).Additive],
  CategoryTheory.Pretriangulated.TriangleMorphism.hom₂ 0 = 0