∀ (C : Type u_2) [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.HasShift C ℤ]
  [inst_2 : CategoryTheory.Limits.HasZeroObject C] [inst_3 : CategoryTheory.Limits.HasZeroMorphisms C] {X Y : C}
  (f : X ⟶ Y),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.Pretriangulated.contractibleTriangle X).mor₁ f =
    CategoryTheory.CategoryStruct.comp f (CategoryTheory.Pretriangulated.contractibleTriangle Y).mor₁