∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] {R : CategoryTheory.Functor Cᵒᵖ RingCat}
  {M₁ M₂ : PresheafOfModules R} {f : M₁ ⟶ M₂},
  (∀ ⦃X : Cᵒᵖ⦄, Function.Surjective ⇑(CategoryTheory.ConcreteCategory.hom (f.app X))) → CategoryTheory.Epi f