∀ (C : Type u_1) [inst : CategoryTheory.Category.{v_1, u_1} C] [inst_1 : CategoryTheory.HasShift C ℤ]
  (X : CategoryTheory.Pretriangulated.Triangle C),
  ((CategoryTheory.Functor.mapTriangleIdIso C).hom.app X).hom₂ = CategoryTheory.CategoryStruct.id X.obj₂