∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {F₁ F₂ : CategoryTheory.Functor C (Type w)}
  {A : CategoryTheory.Subfunctor F₁} (f g : A.toFunctor ⟶ F₂),
  CategoryTheory.Mono (CategoryTheory.Subfunctor.equalizer.ι f g)