∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.HasShift C ℤ] (X₁ X₂ : C)
  [inst_2 : CategoryTheory.Limits.HasZeroMorphisms C] [inst_3 : CategoryTheory.Limits.HasBinaryBiproduct X₁ X₂],
  (CategoryTheory.Pretriangulated.binaryBiproductTriangle X₁ X₂).obj₁ = X₁