∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Preadditive C]
  [inst_2 : CategoryTheory.Limits.HasZeroObject C] [inst_3 : CategoryTheory.HasShift C ℤ]
  [inst_4 : ∀ (n : ℤ), (CategoryTheory.shiftFunctor C n).Additive] [inst_5 : CategoryTheory.Pretriangulated C]
  (t : CategoryTheory.Triangulated.TStructure C) (n : ℤ) {X Y : C} (φ : X ⟶ Y) (H : ∃ f, f.hom₂ = φ),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.Triangulated.TStructure.TruncAux.triangle✝ t n X).mor₃
      ((CategoryTheory.shiftFunctor C 1).map H.choose.hom₁) =
    CategoryTheory.CategoryStruct.comp H.choose.hom₃
      (CategoryTheory.Triangulated.TStructure.TruncAux.triangle✝¹ t n Y).mor₃