∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] [inst_1 : CategoryTheory.Abelian C]
  (S : CategoryTheory.ShortComplex.SnakeInput C) {Z : C} (h : S.L₃.X₃ ⟶ Z),
  CategoryTheory.CategoryStruct.comp S.v₁₂.τ₃ (CategoryTheory.CategoryStruct.comp S.v₂₃.τ₃ h) =
    CategoryTheory.CategoryStruct.comp 0 h