∀ (C : Type u_2) [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Preadditive C]
  (F : CategoryTheory.Functor C C) [inst_2 : F.Additive] (A₁ A₂ : CategoryTheory.Endofunctor.Algebra F) (a b : A₁ ⟶ A₂),
  a - b = a + { f := -b.f, h := ⋯ }