∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.HasShift C ℤ]
  [inst_2 : CategoryTheory.Limits.HasZeroObject C] [inst_3 : CategoryTheory.Limits.HasZeroMorphisms C] (X : C),
  (CategoryTheory.Pretriangulated.contractibleTriangle X).obj₁ = X